Monday, July 28, 2014

Guest Post: "Before They Took Off - A Study of Feathers and How Birds Gained Flight" by my daughter Julia

I am elated and honored to present this guest post to the followers of my blog, written by my daughter Julia, who attends a major American university. The subject matter is the developmental evolution of feathers. The post was a final paper for her course on dinosaurs. A few additional images and captions have been added for this on-line presentation. 

Which came first, the feather or the bird? The long-cherished view of how and why feathers evolved has been challenged and overturned. It is now believed that feathers evolved in small carnivorous, bipedal dinosaurs - nonavian theropods -  that lived on the ground well before the origin of birds and the acquisition of flight.


This feather from a New England Wild Turkey (from Chestnut Hill, MA) bears a pennaceous distal portion, a plumulaceous proximal portion and intermediary afterfeathers.


THE GREAT MYSTERY
Feathers are the most complex integumentary structures that have been observed on any vertebrate in earth’s history. Their incredible diversity ranges from the simplest forms to some of the most extravagant pieces of artwork present in nature, and their evolutionary history spans back millions of years to the age when dinosaurs roamed the earth during the late Triassic period of the Mesozoic era. In addition to their striking appearance and ubiquitous nature, there is a great deal of mystery surrounding the origin of feathers.



From Wikimedia Commons


The most obvious assumption would be that feathers evolved for flight; however, when we take a closer look at the fossil record we can see that this is not the case. Contrary to popular belief, these incredible structures did not first evolve for flight, but instead evolved in a series of developmental stages that were fueled by a number of evolutionary novelties, the last of which was powered flight.

Feathers evolved in the theropod dinosaurs within the saurischian group, although it is important to note that other dinosaurs outside the theropods have been found with structures bearing resemblance to protofeathers. These taxa include ornithischians such as the heterodontosaurid Tianyulong and the ceratopsian Psittacosaurus.


The cat-sized ornithiscian Tianyulong sporting long, hollow, primitive protofeathers.
Did feathers evolve independently or were they derived from filaments of a common ancestor to all dinosaurs?
Photo from scienceblogs.com


Although it may seem that the structures between these clades are related to one another, without any evidence in the fossil record of taxa ancestral to both of these groups with primitive feathers, the most reasonable assumption is that these look-alike structures are just an example of convergent evolution.


Simplified dinosaur lineage showing the appearance of feathers in their various forms of development.
The confusing picture of feather origins became somewhat fuzzier with the discovery of protofeathered ornithiscians (left side), a distinction previously reserved for sauriscians (right side).
From scienceblogs.com


FALSE LEADS
Although minor variations in the appearance of modern feathers can easily be explained in evolutionary theory, it is much more difficult to explain the appearance of entirely new structures in the fossil record. Due to this difficulty, there have been many hypotheses of the origin of feathers that have been proven unlikely. One of the more popular hypotheses states that feathers evolved from the elongation and division of scales.
In this theory, after scales first elongated, they produced fringed edges and then finally branched developing hooked barbules.


Impression of scales of Tyrannosaurus Rex in sandstone

                 
However, this theory was proven incorrect by the lack of similarity between the developmental stages of the two structures. As seen below, feathers first develop a cylindrical sheath that later uncurls - meaning the front and the back of the planar sides of the feather stem from the inside and outside of the initial tubular shaft. The planar sides of the scale on the other hand stem from the top and the bottom of the primary epidermal outgrowth that forms the scale. Due to the contrasting developmental nature of these two structures, it is unlikely that feathers could have evolved from scales.

                                               
A feather emerges from its sheath, a temporary structure that protects the growing feather. At the same time, the internal epidermal layer becomes partitioned into a series of compartments called barb ridges, which later grow to become the barbs of a feather.
Modified from Prum and Brush, Scientific American, 2003.



THE FEATHER EXAMINED
So if not scales, what exactly are feathers? When looking closely at feathers, it can be observed that like other integumentary appendages, such as hair, nails and scales, feathers grow from controlled proliferation of cells in the epidermis, which create keratin proteins. In modern feathers, the rachis is the main, tubular shaft of the feather from which individual branches or barbs emanate. These barbs are also branched with tiny-paired filaments known as barbules, which fuse to the shaft of the barb or ramus.



The Anatomy of a Feather
The stiff, central shaft of a feather is divided into two regions. The hollow calamus is closest to the body and is vaneless. The distal end of the shaft is the rachis, which is solid and contains flat vanes. Vanes are comprised of a series of parallel branches called barbs with short branchlets called barbules. Tiny hooklets tie the barbules and ultimately the barbs together. The structure makes the feather strong and light.
Illustration by Sabine Deviche from askabiologist.asu.edu


There is also a large amount of diversity in the world of feathers, but these variations can be organized into two blanket groups - plumulaceous and pennaceous feathers. The plumulaceous feather, also known as the downy feather, consists of a simple rachis that hosts a fluffy jumble of barbs, each of which has long spindly barbules attached to it. These feathers are lightweight and provide great insulation. Pennaceous feathers on the other hand are the stiffer aerodynamic feathers that can be observed covering the bodies of birds - the iconic feather of a quill pen. The barbs of these feathers are tightly packed together in a planar fashion.


The amazing diversity of feathers serves a wide array of functions that include courtship, thermoregulation, brooding, camouflage and flight. This diversity to accomplished by variations in the shape of the feather's component structures and of course color. Most feathers are pennaceous - penlike (left) or plumulaceous - downy (right). Closed pennaceous feathers with tiny interlocking hooklets on the barbules are essential for flight. Asymmetrical vanes create aerodynamic forces. Plumulaceous feathers have no vane and possess a rudimentary rachis and a jumbled tuft of barbs with elongated barbules. They provide insulation.
Modified from Prum and Brush, Scientific American, 2003.

      
THE EVOLUTION AND DEVELOPMENT OF THE FEATHER
There are thousands of morphological presentations of feathers represented in the earth’s fauna, varying in size, shape and color; however, each one of these diverse structures that coats the living theropods developed from the same simple design. The feather evolved through a series of incremental morphological changes, which occurred over millions of years.


Stage 1 - a hollow cylinder or protofeather
The first of these stages began from the elongation of the placode (a thickening in the endothelium which gives rise to various integumentary structures), which created a long and rigid hollow tube extending outwards from the skin, the first feather.

Stage One - the first feather, a hollow cylinder that resembles the calamus of a modern feather. The follicle originates with a cylindrical epidermal invagination around the base of the feather.
Modified from Prum and Brush, Scientific American, 2003.

This monofilamentous stage of feather evolution is represented by the tyrannosaurid Dilong paradoxus, which was found in the “Feathered Dinosaur Beds” of Liaoning, China. The fossilized tyrannosaur was found to have filamentous integumentary structures as seen below. 


Protofeathers of the tyrannosaurid Dilong paradoxus
Traces of filamentous integumentary structures on the caudal vertebrae with line-drawings below.
From Xu et al, 2004. 

From the Early Cretaceous of China, Dilong paradoxus, a T-rex cousin at the base of the tyrannosaurid tree, sported a partial coat of hair-like feathers. Although predicted by several paleontologists, the discovery marks the first time feather-like structures have been observed on a tyrannosaurid. With this find, we can see an evolutionary transition from typical coelurosaurians to highly specialized large tyrannosaurids. It's unlikely that large tyrannosaurids were covered with feathers. They didn't require insulation for their warm bloodedness based on their size. Perhaps only juveniles were feathered and in the cranium rather than the post-cranium.
From trexfeathers.co.uk

A model restoration of the Late Cretaceous tyrannosaurid Lythronax argestes from the Wahweap Formation of Utah. Note the hypothesized protofeathers that adorn the posterior cranium.
From National Geographic.com


Stage 2 - unbranched barbs attached to a calamus
The second stage of feather evolution began with the differentiation of the follicle collar. In this stage, the follicle collar split into an inner layer of longitudinal barbs, and an outer layer that consisted of a protective sheath, making up the calamus. From the calamus there extended a tuft of branched barbs, creating the first structure visually reminiscent of a plumulaceous feather.

Stage Two - unbranched barbs attached to a calamus.
The inner, basilar layer of the collar differentiated into longitudinal barb ridges that grew unbranched keratin filaments. The thin peripheral layer of the collar became the deciduous sheath. The resulting mature feather resembled a tuft of unbranched barbs with a basal calamus.
Modified from Prum and Brush, Scientific American, 2003.


This morphotype is known from the basal dromaeosaur Sinornithosaurus millenii. The feathers from this taxon are diffusing arrays of filaments lacking a prominent central rachis.


The filamentous feather of Sinornithosaurus millenii (Chinese bird-lizard) from the dorsal surface of the snout that converge at a single base with accompanying line-drawing.
From Xu et al, 2001.

 Sinornithosaurus millenii from the Early Cretaceous of China
From picsearch.com

Stage 3 - a planar feather with central rachis or with barbules attached to calamus
The next evolutionary stage of development has two potential steps. It is unclear through the fossil record which one of these two evolutionary steps occurred first; however, both of these newly developed feathers would eventually lead to the formation of double-branched feathers, which consist of a rachis as well as both barbs and barbules. These feathers were planar as well as open pennaceous, meaning that the barbules did not yet interlock to create a closed vane.


Stage Three - has two potential steps, a planar feather with unbranched bards fused to a central rachis
or a feather with barbs and tiny branches called barbules attached at the base to a calamus, either of which could have occurred first. Both are required prior to Stage 4. The evolution of helical displacement of barb ridges within the collar (upper image) resulted in the origin of the rachis, which is formed by the fusion of barb ridges on the anterior midline of the follicle. The evolution of paired barbules within the peripheral barbule plates of the barb ridges (lower image) created the branched barbs with rami and barbules.
Modified from Prum and Brush, Scientific American, 2003.


The first possible step (uppermost feather above) of this third stage is the origination of barbules extending from each individual barb in the tuft. A taxon bearing this variation of the feather is the basal therizonosaurid theropod, Beipiaosaurus. The feathers of this taxon are broad and filamentous feathers that have been elongated.


In the therizinosaurid Beipiaosaurus each individual feather is represented by a single broad filament. The images above show their attachments to the theropod's tail.
From Xu et al, 2008.

The sickle-clawed, primitive therizinosaurid Beipiaosaurus from the Early Cretaceous of China
From Wikimedia Commons

The second step of stage three in feather evolution is the helical growth of barb ridges, which lead to a planar feather with unbranched barbs fused to a newly formed central rachis.


Stage 4 - a closed symmetric pennaceous vane
At stage four, the differentiation of barbules began to take place. This led to the formation of hooked barbules, which allowed for an interlocking mechanism between adjacent barbs, thus creating the closed feather vane, and the fourth step in the pathway to flight feathers.

Stage Four - closed pennaceous vane with hooklets on one barbule attached to grooves on the barbules of adjacent barbs. The evolution of differentiated distal and proximal barbules created the closed, pennaceous vane. Terminally hooked pennulae on the distal barbules evolved to attach to the simpler proximal barbules
of the adjacent barb to form the closed vane.

Modified from Prum and Brush, Scientific American, 2003.


This stage can be observed in a close relative of the Archaeopteryx, the theropod Caudipteryx (meaning "tail-feather"), of which feather impressions have been identified as having an obvious rachis as well as a herringbone pattern within the barbs that is accepted as a close-vaned feather. The closed-vane surface of this feather, impermeable to air, later assisted in enhancing the effectiveness of each wing stroke when birds finally developed flight, and allowed for many of the specializations we see in stage five of feather evolution, such as the formation of the asymmetrical feather.


The speedy Caudipteryx possessed a closed-vaned feather but could not fly.

Peacock-sized Early Cretaceous Caudipteryx from China
From Wikimedia Commons 


Stage 5 - a closed asymmetrical vane
In the last stage of feather evolution, the asymmetrical flight feather, resembling the feathers of many modern birds alive today, began to develop. This occurs through the addition of barbs to just one side of the rachis. 


Stage Five - closed asymmetrical vane resembling a modern flight feather
Asymmetrical flight feathers with vanes of different widths evolved by the lateral displacement of the new barb ridge locus from the posterior midline of the collar toward either side (stage Va). Vane asymmetry could have evolved any time after the origin of a planar vane (stage IIIa), but, prior to stage Va, these asymmetrical feathers could not have been closed and pennaceous or functioned in flight. With this fifth stage, the popular and enduring theory that feathers evolved primarily or originally for flight is put to rest. Feathers were "exapted" for their aerodynamic function only after the evolution of substantial developmental and structural complexity.
Modified from Prum and Brush, Scientific American, 2003.


Only the most advanced feather shapes have the ability to facilitate flight. The narrow leading edge (outer vane) of the asymmetrical feather is stiff and thin, while the trailing edge (inner vane) behind is flexible and long. This configuration allows the bird to use the tilt of its wings to create lift by adjusting the airflow around them. For this reason, the last step in feather evolution, the asymmetrical feather was crucial to the appearance of flight in the theropod dinosaurs.



The flight feathers of this Great Blue Heron are the long, stiff pennaceous feathers that are symmetrically-paired but asymmetrically-shaped (via a laterally-displaced rachis). Located on the wing (remiges) and the tail (rectrices), they generate thrust and lift, thereby enabling flight. This is also accomplished by an asymmetric wing in cross-section.

Rather than being an adaptation for powered flight, feathers must have evolved for a different purpose and then been modified into a more specialized structure in order to lift off the ground. The phylogeny of each of these evolutionary steps can be observed below.


Combined cladogram of theropod dinosaur and feather evolution
Stage 1 - a hollow cylinder; Stage 2 - unbranched barbs attached to a calamus; Stage 3 - a planar feather
with central rachis or with barbules attached to the calamus; Stage 4 - a closed symmetric pennaceous vane;
and Stage 5 - a closed asymmetrical pennaceous vane.
Modified from Prum and Brush, Scientific American, 2003. 


MOLECULAR SUPPORT FOR FEATHER EVOLUTION
When looking at the development of the feather, it is also important to consider what is happening on the molecular level, and how that results in such complex structures. In the case of the feather, there are two important genes that assist in pattern formation - sonic hedgehog (Shh) and bone morphogenetic protein 2 (Bmp2). These genes have an essential role in development and are used repeatedly for the creation of the feather starting with cell proliferation, which is induced by the Shh protein. Bmp2 then helps regulate the extent of proliferation and assists in cell differentiation.

In the newly created placode, the Shh and Bmp2 proteins are expressed in a polarized anterior-posterior fashion, and then subsequently expressed at the tip of the cylindrical feather-germ to facilitate elongation. Next, the genes are expressed in the epithelium separating the barb ridges that are beginning to form, and they begin to establish a growth pattern for each ridge. In pennaceous feathers, the signaling of Shh and Bmp2 proteins then lay down the pattern needed for the helical growth of barb ridges, and the formation of the rachis. In plumulaceous feathers the proteins create a pattern for the growth of barbs much simpler than that in pennaceous feathers. This signaling pattern can be observed in the following figure.


The different expression of the two proteins, Bmp2 and Shh, in disks of skin cells called placodes
in embryonic reptiles including birds.
From bio.miami.edu/dana/107/107F11_16.html

CREATING AN EVOLUTIONARY MODEL
So, if powered flight did not come into play until the very end of feather evolution, what fueled the initial changes that brought it to that point? There is still much controversy on this topic, as it is highly difficult to test; however, there are many hypotheses of different evolutionary novelties that seem to make sense in pushing the development of feathers to the extreme.


One of these initial functions was suggested to be thermal insulation, as the long tangled barbules of the plumulaceous feather provide great lightweight coats, and provide their insulation much more efficiently than reptilian scales. This insulation also helps in incubating eggs; therefore, brooding is also considered a possible function of these non-avian feathers.


Discovered by Roy Chapman Andrews in Mongolia in 1925, this brooding oviraptorid Citipati osmolskae specimen from the American Museum of Natural History in NYC displays its hind limbs, caudal vertebrae and a portion of the pelvic architecture on a nest of eggs. 
From Dinoguy2 of Wikimedia Commons


Water repellency would have been another use of feathers with a closed vane, as the interlocking nature of the barbicels creates a barrier against water. Sexual signaling is also an important function of feathers; feathers can be used as species recognition as well as to send visual signals for sexual or social behavior. Many modern birds use their vibrantly colored displays to inform potential mates they are healthy and physically fit, making them better candidates for reproduction; for this reason, sexual selection tends to favor such elaborate traits. 

OTHER ADAPTATIONS FOR POWERED FLIGHT
When discussing the evolutionary path to powered flight, there are many anatomical requirements and system modifications that must be considered in addition to the asymmetrical flight feather. One of these important adaptations is a well-developed pectoral girdle, which provides the force necessary to push the air and oppose gravity, thus propelling the animal forward.



The avian pectoral girdle is formed by the bones of the sternum (breastbone), coracoid, scapula and the furcula (a pair of fused-clavicles, the "wishbone"). The keeled-sternum is the paramount modification of the avian skeleton for flight and the site of attachment for the muscles of flight (the breast meat!). The clavicle (wishbone) flexes during flight and likely facilitates flight or respiration.
From avesvitae.org 

The pectoral girdle is made up of the coracoid, scapula, furcula and a keeled sternum. In the shoulder of the bird, the scapula and the coracoid articulate with the humerus to form the foramen triosseum. Through this foramen the tendon of the supracoracoideus muscle passes to insert on the humerus and create a pulley system that raises the wing as the muscle is contracted. Contraction of the pectoralis muscle draws the humerus and wing downward. 



Although the limbs of both mammals and birds possess the same basic osseous architecture, only mammals possess deltoid and trapezius musculature that raises the arm. Birds, on the other hand, utilize paired supracoracoideous-pectoralis muscles (the "breast meat") that originate from the keeled sternum. The former is the elevator and the latter, the depressor of the humerus - via the tendons that sling through the foramen triosseum. Voila! Flight. 
From Wikimedia Commons


This highly derived pectoral structure was not observed in Late Jurassic Archaeopteyx ("ancient feather or wing"), considered to be transitional between feathered dinosaurs and modern birds. The keeled sternum of the modern bird uses its large surface area for a more effective attachment of the pectoralis muscle that powers the down stroke of the wing. The aerodynamic nature of the keeled sternum also allows avian creatures to glide through the air with less resistance, allowing for better flight stamina. 


The Berlin specimen of Archaeopteryx lithographica from the Solnhofen limestones had been celebrated as the oldest known bird, but older potential avialans have been identified. The impression of flight feathers that escaped early examiners are evidence that the evolution of feathers began before the Late Jurassic. Notice the reptilian sharp teeth, three fingers with claws, long bony tail, large flight-capable brain, hyperextensible "killing claw" second toes, frond tail and lack of a power-generating keeled sternum. Its asymmetrical feathers and broad tail feathers imply that it was capable of flight, but opponents argue it was a tree-dwelling glider or perhaps a downstroke-only flap-assisted glider.
From Wikimedia Commons

Artist's impression of Archaeopteryx from the Jurassic of Germany
From The Westside Story


The development of pneumatic bones in theropod dinosaurs was also extremely important for the facilitation of flight. Pneumatic bones contain air sacs that are hooked up to the bird’s respiratory system. These sacs assist in respiration, as well as create a lightweight skeletal structure ideal for flight. 




Feathers were not enough to lift the dinosaurs off the ground; they needed a combination of many other anatomical specializations that favored flight to allow them to facilitate lift off. The lack of some of these adaptations for flight in feathered dinosaurs further emphasizes the idea that feathers could not have initially evolved for powered flight.

THE MYSTERY SOLVED?
The evolution of the feather is an intriguing subject on the list of structures of which the ancestral condition is not entirely obvious upon first glance; however, through the close study of the fossil record, various relationships between modern birds and non-avian theropods can be made. By observing such taxa within the dinosaurian group theropoda, one can arrive at the conclusion that feathers are not an adaptation for powered flight, but rather powered flight is the last of a number of evolutionary novelties that pushed the development of the feather to its highly specialized form. 



From Evolution of Dinosaurs into Birds.com


Well done, Julia!

WORKS CITED
Brush, A.H., R.O. Prum. 2003. Which Came First, the Feather or the Bird? Scientific American: 86-93

Guo, Y, X. Xu. 2009. The Origin and Early Evolution of Feathers: Insights from Recent Paleontological and Neontological Data. Vertebrata Palasiatica: 312-320
Jia, C, M.A. Norell, X. Kuang, X. Wang, Q. Zhao, X Xu. 2004. Basal Tyrannosaurids from China and Evidence for Protofeathers in Tyrannosaurids. Nature 431: 680-683
Poore, S.O., A. Ashcroft. 1997. The Contractile Properties of the M.Supracoracoideus in the Pigeon and Starling: A Case for Long-axis Rotation of the Humerus. The Journal of Experimental Biology 200: 2987-3002
Prum, RO., 2002. The Evolutionary Origin and Diversification of Feathers. Quarterly Review of Biology 77: 261-295
Prum, R.O., X. Xu, Z. Zhou. 2001. Branched Integumental Structures in Sinornithosaurus and the Origin of Feathers. Nature 410: 200-203
Ruben, J. 1991. Reptilian Physiology and the Flight Capacity of Archaeopteryx. Evolution 45: 1-17
Stettenheim, P.R. 2000. The Integumentary Morphology of Modern Birds-An Overview. American Zoology 40: 461-477
Wake. D.B. H. You. X. Zheng, X. Xu. 2009. A New Feather Type in a Nonavian Theropod and the Early Evolution of Feathers. Proceedings of the National Academy of Sciences of the United States of America 106.3: 832-834
Witmer, L. 1990. The Craniofacial Air Sac System of Mesozoic Birds (Aves). Zoological Journal of the Linnean Society 100: 327-343
Zimmer, C. 2011. Evolution of Feathers. National Geographic Magazine

Sunday, June 29, 2014

Geological Legacies of the Paris Basin: Part II – Subterranean Limestone Quarries and Catacombs of Paris

"...Paris has another Paris under herself…which has its streets, its intersections,
its squares, its dead ends, its arteries, and its circulation”
Les Miserables, Victor Hugo, 1862

 



For a discussion of the tectonic evolution of the Paris Basin, its Lutetian stratigraphy and the gypsum deposits of the Right Bank, please visit my previous post entitled "Geological Legacies of the Paris Basin: Part I - Plaster of Paris, the Windmills of Montmartre, the Park of Buttes-Chaumont and a New Artistic Creativity" here.

PARIS SOUTERRAIN - PARIS UNDERGROUND
Stroll the narrow cobbled streets and broad boulevards on the Left Bank of the old French capital. Enjoy Paris’s beautiful storefronts, its exquisite monuments, museums, parks and stunning architecture. Languish in a sidewalk café or dine in a fashionably chic bistro. For the casual observer, it’s impossible to imagine what lies underfoot – 20 to 25 meters below street level.

Paris is a city of layers – both above ground and below. Its underground has many new additions, while others are vestiges of the past, often lost and forgotten. Some are accessible to the public, and others have been sealed for an eternity.

There are Roman Empire foundations and more recent wartime shelters, medieval basements and mysterious church crypts, musty wine cellars and shadowy mushroom farms, subterranean shopping malls and modern multi-level car parks. Factor in 1,305 miles of storm drains and sewers, 133 miles of Métro and RER railway tunnels, and countless miles of utility lines and pipes for water, gas, electricity and telephone. Standing on the streets of Paris, you'd never suspect what exists below you unless you looked at a map of the underground that mirrors the landscape above.


Modified from the Atlas du Paris Souterrain – a highly-recommended source of information!

 
Yet, there exists an even deeper layer! On the Right Bank, the buttes of Montmartre and Belleville are riddled with gypsum quarries. On the Left, Paris is honeycombed with a labyrinth of over 200 miles of cavernous limestone quarries replete with a macabre section known as the Catacombs – after the ones in Rome.  

The Catacombs is a dimly lit, musty maze of galleries and corridors lined with the bones of 6,000,000 (seven by some counts) disinterred Parisians. In one section, a water-filled well contains the stratigraphic contact of the Lutetian age 45 million years ago. How did these two “cities” evolve? How do they co-exist? A luminous City of Light above another of shadows and darkness.



 
GEOLOGIE PIEDS DE PARIS - PARIS’S GEOLOGY UNDERFOOT
The city of Paris occupies a tiny portion of the extensive Paris Basin – a 140,000 square kilometer shallow epicontinental trough of flat valleys and low plateaus in the north of France. On a larger scale, the depocenter of the Anglo-Paris Basin that spans the English Channel into Great Britain resides on the continental shelf of the Eurasian plate. Its foundation is a Late Proterozoic Cadomian-late Paleozoic Variscan crystalline basement. Please visit my post Part I for the Paris Basin’s juicy tectonic details here.


Paris (red dot) within the extensive Anglo-Paris Basin on a
Jurassic through Neogene Surficial Geology Map
 
During the late Paleozoic, the basin began to form subsequent to extensive orogenic collisions that formed Pangaea in the western hemisphere. By the end of the Mesozoic, the basin (along with the assemblage of France, Belgium, Great Britain, Scandinavia and Western Europe) was tectonically transported to the eastern hemisphere on the Eurasian plate when Pangaea fragmented apart and the Atlantic Ocean opened its waters.

The basin’s strata were deposited in a multitude of Tertiary age transgressions and regressions of tropical seas that flooded the epicontinent of Western Europe. Formed in a mixed environment of marine, coastal, lagoonal and freshwater conditions, deposition was followed by compaction, cementation and eventual lithification.


Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.

The sedimentary rocks that formed - during the Eocene epoch in particular - built the city of Paris: Bartonian age gypsums (gypse) for plaster of Paris on the Right Bank (north side of the river Seine) and Lutetian age limestones (calcaire grossier), chalks (craie) for lime-based cements and paints, clays (argile) for tiles and bricks, and sand (sable) for masonry on the Left Bank (south of the river). The deposits on each side of the river Seine are between two low plateaus, Montmartre and Montparnasse. Both banks were exploited from under the city, as Paris grew and expanded on the surface.






ANTICLINE OF MEUDON
Fortuitously for Paris’s architectural future, the axis of the Tertiary age anticline of Meudon (red dotted line below) passes south of the city. The flexure allowed for the excavation of Paris’s geological bounty of gypsum from the Right Bank and deeper, coarse limestone from the Left.


Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013


The geologic transect (black line above) extends across the basin from north to south and is represented cross-sectionally below. Note the availability of Lutetian limestone (calcaire grossier) south of the Seine on the Left Bank and gypsum (gypse) north of the Seine on the Right Bank in Montmartre. The vertical scale across the basin is greatly exaggerated making Montmartre appear like the Matterhorn.


Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013


TWO MAJOR EXPLOITATION ZONES OF PARIS
Thus, gypsum has been extracted in the hills of Paris on the Right Bank from Menilmontant, Montmartre and Buttes-Chaumont areas of the 18th, 19th and 20th arrondisements, respectively. Limestone was mined under the small Parisian hills of Montparnasse, Montsouris, Montrouge, the Butte aux Cailles and the Colline de Chaillot, largely on the Left Bank.
 


Topographical Considerations of Paris
Modified from Arch.ttu.edu


ANCIENNES CARRIÈRES DE PARIS - ANCIENT MINES OF PARIS
The areas of Right Bank gypsum (green clusters) and largely Left Bank limestone (red) exploitation can be seen highlighted on this old Paris map of 1908. The direction of flow of the River Seine is shown in black arrows.

 
Wikipedia
 

 
THE ROMAN CITY OF LUTETIA
By 53-52 BC, the Romans had conquered Gaul (roughly France and Belgium) and the Celtic Iron Age tribes living in the region. Within the Paris Basin, that included the Parisii, living on the banks of the river Seine. The Romans called their settlement on the hills south of the river Lutetia Parisiorum or Lutece in French. The name was derived from a Parisii word meaning marsh or swamp. In turn, geologists borrowed the name for the Lutetian age - a division of the Eocene epoch of the Cenozoic Era- the time in which the limestone called “Paris Stone” formed – 47.8 to 41.3 million years ago.
 
The decision to settle above the banks of the Seine was governed by its ideal location for trade, defense and availability of raw materials especially water and the limestone for Roman buildings, military fortifications and roads. The Roman and Medieval era that followed produced lasting design elements for the development of the city from the Renaissance through the 21st century.
 
Please note the Roman open quarries (right) in the vicinity of the River Bievre near its confluence with the Seine (lower right), and the Arenes de Lutece amphitheater. As a modern reference, the island in the middle of the Seine in the upper right corner is Île de la Cité that houses the Cathedral of Notre Dame.
 
 
 
 
A DOZEN CENTURIES OF LIMESTONE EXPLOITATION
The Romans in the 1st century and the early Parisians through the end of the 12th century acquired coarse limestone for structures in the most instinctive of ways – from above ground where it was most convenient. It was removed from open quarries (carrières à ciel ouvert) where it had been exposed by erosion such as the region of the Seine’s ancestral tributary, the Bievre (see above). The technique was primitive, but the rock was readily available and had existing natural fractures that facilitated its extraction.
 
One such quarry, virtually unrecognizable today, lies within the heart of Paris beneath the Arena of Lutece, a partially restored Roman amphitheater. Once considerably larger, the majority of the arena’s limestone has been repurposed into structures subsequently built throughout the millennium.
 
 


MINING GOES UNDERGROUND
By the end of the 12th century, medieval Paris had become a medium-size, walled city with a population of 25,000 surrounded by countryside of farms and vineyards. The extraction of surface limestone was gradually replaced by underground workings to satisfy the sharply increased needs for building construction such as Notre-Dame Cathedral, the Louvre Palace and the ramparts of the city.

Mining below the surface also minimized the excavation of overburden, allowed deeper fine-grained deposits to be reached and conserved topsoil for farming immediately around the growing city. The first underground excavations were essentially extensions of the open quarries by digging horizontally into a hillside exposure (left diagram).
 
Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013
 
 
PILIERS TOURNES
The first mining method employed the “room and pillar” technique, called piliers tournes. After a horizontal tunnel was excavated, perpendicular and then parallel tunnels were added (right diagram). The result was a maze of interconnecting passageways with the weight of the ceiling supported by a grid of massive columns of untouched, solid limestone. It helped to prevent collapse of the undermined roof, but a significant portion of usable excavated material was lost.
 
In the 15th century, vertical wells were sunk and then tunnels were dug horizontally from there. In order to raise limestone blocks to the surface, wheeled wooden winches reminiscent of “squirrel” wheels were driven by workers climbing rungs, oxen or horses to raise blocks of limestone vertically. The system could haul up large slabs that weighed as far as 30 meters down. 
 
Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013
 
 
These mining techniques were also used on gypsum deposits for plaster of Paris in Montmartre and the Belleville hills on Paris’s Right Bank. Although artificially engineered, the grotto at the Park of the Buttes-Chaumont is reminiscent of the cathedral-like excavation structures that undermine the region. Please visit my previous post regarding gypsum excavation on the Right Bank here.
 
 
 
 
 
HAGUES ET BOURRAGES AND PILIERS A BRAS
In the 16th century, the mining method of hagues et bourrages was employed that was economically productive and structurally sound. Instead of tunneling horizontally into the exploited table of limestone, miners would extract stone progressively outward from a central point. When the ceiling became sufficiently unsupported, a line of stacked piliers a bras was erected from the floor to the ceiling. When extraction continued outward, a second line of stone columns was added, which were then transformed into walls or hagues as the space in between was backfilled with waste rubble or bourrage.
 


For a fantastic and imaginative 3-D tour of the evolution of Paris beginning with the early Celtic settlement, check out the video here.  A fine appreciation will be gained for the volume of limestone that was extracted beneath the Left Bank during the building of the city.
 
SUBSIDENCE SINKHOLES ON MINED-LAND
The first underground limestone quarries were located in Paris's suburbs (faubourgs) on the Left Bank. As the city continued to grow, new underground quarries with interconnecting galleries were developed on the city’s expanding periphery. Old abandoned quarries fell into oblivion and were gradually built over.
 
Although the undermined state of the Left Bank was known to city architects in the early 17th century, Parisian’s became painfully aware of their precarious existence over the subterranean voids when they began to cave in. At first many thought it to be the work of the devil. Called subsidence sinkholes (fontis in French), the cave-ins varied in size with some affecting houses and others affecting entire streets.
 
 
Formation and Evolution of Subsidence
A fontis is a cavity that develops when the roof of a subterranean gallery caves in.

A cloche is the rounded top of the rubble pile.
Modified from Daniel Munier and from M. Vire
 
The arched void forms that migrates upward as the ceiling rocks gradually tumble in. When the sinkhole finally breaks through the surface, the rounded top of the rubble pile or cloche can be viewed within the sinkhole from above - giving the cavity that has formed a bell shape. These sinkholes should not be confused with those that occur in a karstic landscape, which develops under a cover of soluble rocks - also limestone - via acidic water that has acquired atmospheric carbon dioxide.   
 
CATASTROPHE IN THE MOUTH OF HELL
When the largest collapse occurred in 1774, a wave of panic spread through Paris. A giant sinkhole catastrophically swallowed a busy Parisian neighborhood including roads, buildings, houses, horses, carriages, oxcarts and throngs of people along Rue d’Enfer (now called Boulevard Saint Michel near Avenue Denfert-Rochereau). Appropriately, enfer is the French word for “hell,” and the gaping hole in the earth became known as the “mouth of hell.” The quarries that built the city of Paris were literally threatening to destroy it - neighborhood by neighborhood.

How ironic! The limestone that went into the construction of Notre-Dame, the Palais-Royal and the mansions of the Marais on the surface of Paris actually had come from the quarries beneath Rue d’Enfer – now taking revenge upon the city.

Explographies.com
 
“Paris (had) begun to devour its own foundations – sand for glass and smelting,
gypsum for plaster, limestone for walls, green clay for bricks and tiles.”
From Graham Robb’s “Parisians: An Adventure History of Paris”

  

THE MAN WHO SAVED PARIS FROM SINKING
In response to the fear of collapse, King Louis XVI designated a commission to investigate the state of the Parisian underground on April 4, 1777. It was called the Inspection Unit for Quarries Below Paris and Surrounding Plains. The head of the newly minted office - appointed by the King by chance of fate only a few hours before the collapse - was an architect named Charles-Axel Guillaumot, who held the position of General Inspectorate of the Quarries (IGC) until his death in 1807 - in French, Inspection Générale des Carrières.
 
 
“Guillaumot inspected the "gaping wound as an explorer
could contemplate the shores of a new continent.”
Author Graham Robb


This “Savior of Paris" that the city owes so much set about to inspect and map the fragile voids under the entire city, many of which were illegal and uncharted but most abandoned and forgotten. His goal was to excavate them where needed and reinforce (consolidate) them from future collapse. Virtually every chamber was mapped and assigned a name that corresponded to the street above. The inspected walls still bear his chiseled signature, a "G" and date.

 


 
Following in the tradition of Guillaumot, engineers from the Inspection des Carrieres generally signed and dated their consolidation projects by carving their initials, order number and the years the work was carried out into the walls. Fleur-de-lis, the royal symbol of the French Empire, were obliterated from most of the signatures during the French Revolution.
 
A DOUBLED PARIS
In order to safeguard public roads and of course the King’s properties, Guillaumot erected pillars from the quarry floors to their ceilings, “retrospectively-created foundations for the edifices built on the surface” (Gilles Thomas). The result was that every undercut surface street was doubled by a gallery that followed the same layout. In a sense, Paris became a mirrored city with one above ground and the other below. This allowed the evolution of subsidence voids to be monitored and shored up as needed. The same can be said of the modern city of Paris with its underground double. Here's an example from the 13th arrondissemont.
 
 
From DecodingParis.com
 
In Guillaumot’s own words:
 
“To monitor the preservation of these constructions at all times,
It was necessary to render them accessible; to this effect,
a gallery wide enough to allow passage of construction materials was left under
and within the public way; at the gallery’s farthest point, another wall was built.
Perpendicular galleries were dug here and there to enable communication between
both sides of the public way and to allow movement from one gallery to the next.”
(Memoirs on the Work Ordered in Quarries in Paris and Adjacent Plains, 1804)
 
LES CIMETIÈRE DES SAINTS-INNOCENTS - THE SAINTS-INNOCENTS CEMETERY
Another peril was threatening the city – an insidious one that had become equally intolerable and every bit as dangerous. Paris’s cemeteries had become horrifically overcrowded. The earliest burial grounds were on the southern out-skirts of the Roman-era city on the Left Bank - outside the city! By the 4th century, burials had moved to the Right Bank on filled-in marshland - within the city. In particular was the property of the Saints Innocents church in 1130 - named after the biblical narrative of the "Massacre of the Innocents" by Herod the Great, the Roman-appointed King of the Jews.
 
No larger than a city block and literally within a few blocks of Notre-Dame in the midst of Paris’s densely inhabited area in the current district of Les Halles, problems began to pile up, literally. The foundation of Paris’s first Christian churches were somewhat removed from the center of population and many became crypts for those seeking a final resting place closer to god, a service only available to the wealthy. Common folk were buried outdoors on consecrated clergy property, close to their creator in the "fresh" air. One would think! 
 
 
Map of Paris in 1550
The Cemetery of Saint-Innocents is circled for reference. Click for a larger view.
Modified from OldMapsofParis.com in the Public Domain 
 

 
Saint-Innocents had become Paris’s principal cemetery, although there were countless burial grounds in the city. Saint-Innocents was adjacent to the city’s  principal marketplace Les Halles, where fresh farm products were sold daily. Burying the dead in town was a radical departure from the norm, contrary to logic, sound urban planning and public health.
 
The red ellipse encompasses the Cemetery of Saint-Innocents that included the central burying ground, the church and the surrounded charnel house. Notice the proximity of Saint-Innocents to the central market Les Halles - now known as Forum des Halles. This ambitious, aerial urban map of 1739 before the city’s redesign by Baron Georges Eugene Haussmann is but a small section of Paris with accurate detail of every building drawn down to the windows. You can visit the entire city map here.
 

Turgot-Berez Map Plan of Paris in 1739
Modified from geographicus.com/blog/rare-and-antique-maps/antique-map-of-the-week-the-turgot-bretez-plan-of-paris
 

By the end of the 19th century, the burial ground in Saints-Innocents has become a two and one half meter-high mound filled with over ten centuries of dead bodies largely from Paris’s 22 parishes – perhaps two million. The corpses had accumulated from natural causes, disease (particularly cholera and plague), famine, wars, and the collected remains from hospitals such as the Hôtel-Dieu and the morgue. Other Parisian parishes had their own burial grounds, but the conditions in Saints-Innocents were by far the worst.

LES CHARNIERS - THE CHARNEL HOUSE
In an attempt to relieve the overcrowding, Saints-Innocents was enlarged and surrounded by a high wall. What had begun as a cemetery of individual sepulchers - burial chambers such as crypts and tombs - had become a site for mass graves with large numbers of bodies buried in a single pit. When a mass grave was filled, a new one was initiated. And so on.

To make room for more burials in the 14th and 15th centuries, charniers or charnel houses (from a Latin derivative relating to flesh) were constructed around the burying ground to act as a repository for the overflow of corpses from the burying ground.


Wikipedia


The long dead were exhumed and their bones were tightly packed into the walls and roofs of the charnier galleries. Bones were stacked in an almost artfully decorative pattern, while outside, rotting corpses on the grounds poisoned the air with a nauseating stench. Those living in proximity to the cemetery and certainly those downwind were the first to suffer. Broth and milk were said to sour within hours. The tapestries of merchants in nearby Les Halles discolored quickly. Wine turned to vinegar and resting one’s hand on damp, moldy walls was a risky endeavor. In nearby churches, the generous use of incense was insufficient to mask the foul stink. The French writer Louis-Sébastien Mercier (1740-1814) wrote:
 
“The stench of cadavers could be smelt in almost all churches;
…the reek of putrefaction continued to poison the faithful.
Rats live among the human bones, disturbing and lifting them,
seeming to animate the dead as they indicate to the present generation
they among which they will soon stand...
They (the bones) will soon all turn to chalky earth.”

A close up of the charnel house shows the skulls stacked in the upper tiers, while rotting corpses literally littered the burying grounds. Now lost but recorded in manuscripts, a mural of Danse Macabre or the Dance of Death was painted on the south wall within an alcove of the charnel house. Represented in many languages and countries, the theme dates from 1424-24. No matter one’s station in life, the universality of death depicted in the “dance” is an artistic genre of late-medieval allegory. It was meant to remind people of life’s fragility and the vainness of the glories of their earthly lives. One might think that a view of the burial grounds was likely all that was needed!

 
Wikipedia
  
Further insight into the unhealthy conditions at Saint-Innocents can be gleaned from Mercier’s description of the insalubrious state of affairs at the hospital Hôtel-Dieu on nearby Île de la Cité:
 
“Hôtel-Dieu has all it takes to be pestilential (contagious), because of its damp and unventilated atmosphere; wounds turn gangrenous more easily, and both scurvy and scabies wreak havoc when patients sojourn there. What in theory are the most innocuous diseases rapidly acquire serious complications by way of the contaminated air;
for that precise reason, simple head and leg wounds become lethal in that hospital.
Nothing proves my point so well as the tally of patients who perish miserably each year
in the Paris Hôtel-Dieu…a fifth of the patients succumb; a frightful tally
treated only with the greatest indifference.”
 
LOUIS XVI ISSUES EDICTS
Nothing was done to remedy the intolerable situation until King Louis XV initiated an investigation in 1763. His successor, King Louis XVI, in his first year on the throne in 1775, issued an edict to move the deceased out of the city. The church resisted the notion, which profited from burial fees. Business was good! To reduce the number of burials, the price was increased, something only the wealthy could afford.
 
 
Wikipedia
 
In 1780, a mass grave containing over 2,000 partially-decomposed bodies collapsed under the sheer weight spilling into an adjacent basement on Rue de la Lingerie. The event further heightened concerns for public health and hastened the decision to eliminate Saint-Innocents once and for all.  That same year the edict was issued that forbade burying corpses at Saint-Innocents and all other cemeteries within the city limits of Paris.
 
At a time when Saints-Innocents housed over two million corpses, one major problem had been solved, but a greater one was created. What to do with the overflowing contents of Saint-Innocents?
 
MINE RENOVATIONS AND CEMETERY CLOSURES OFFER A COMMON SOLUTION
Mine consolidations were still under way and included the addition of a network of interconnecting subterranean passageways for access. With the cemeteries closed, Police Prefect Lieutenant-General Alexandre Lenoir supported an idea of moving the dead to the newly renovated corridors to be used as an underground sepulcher. The idea became law in 1785. Saints-Innocents was to be evacuated and converted into the public square that has remained to this day, Place Joachim-du-Bellay – more on that story later in this post.
 
The location for the collective burial ground was a spot designated in popular culture as the Tombe-Issoire within the limestone quarries of the Montrouge Plain outside Paris - more precisely, the suburb of Petit-Montrouge. The region is on the hillsides on the left bank of the Bièvre River mentioned earlier and riddled with limestone quarries at depth. At the time, the commune was outside the city walls of the Wall of the Farmers-General, used primarily for tax collection rather than defensive purposes. It was variously known for its monasteries, religious orders, royal hunting grounds, windmills and, of course, its quarries. Today, there are no famous monuments in the suburb of Montrouge. The major tourist attraction is beneath the quarter! 
 
 
The location of the Plains of Montrouge outside the walls of the city of Paris
 
 
THE CATACOMBS BECOME AN OSSUARY
On April 7, 1786, the grounds of the former quarries of the Tombe-Issoire under the Plain of Montrouge (the burial site of a legendary giant named Issoire slain by William the monk) were sanctified in the presence of the church abbots, the architects of the project and Charles-Axel Guillaumot. On November 16th, Monseigneur Leclerc de Juigne and Archbishop of Paris ordered: 
 
“the removal of the Saints-Innocents Cemetery, its demolition and its evacuation,
entailing the turning of the soil to a depth of five feet and the sieving of earth,
with any remaining corpses or bones to be transported and buried
in the new underground cemetery of the Montrouge Plain.”
Cited in Les Catacombes, etude historique, 1861
 
The Tomb was called the Catacombs of Paris, in French, Les Catacombes de Paris, after the Roman Catacombs. Although Paris’s early limestone quarries date back to the Roman period, the Catacombs do not. And, unlike the Roman Catacombs, they were never excavated for the purposes of burial, only repurposed for burial after the space had been established. The official name for the catacombs is L’Ossuaire Municipal or The Municipal Ossuary.  
 
THE EXHUMATION AND TRANSFER OF BONES
The first transfers of bones from Saints-Innocents to the Catacombs lasted 15 months and continued with the populations of Saint-Étienne-des-Grès, Saint-Eustache, Saint-Landry, Sainte-Croix-de-la-Bretonneries, Saint-Julien-des-Ménétriers and so forth. Continuing to 1814, every cemetery, church ground, crypt and tomb of Paris was nocturnally emptied of its human remains. In total, over six million Parisians were withdrawn and transported to their new “haven of peace” beneath the Plains of Montrouge. The exact number is impossible to determine. The estimate is based on the number of burials up to the year 1860 when the contents of the last graves were transferred to the ossuary. 
 
The enormous transportation of bones was scrupulously ritualized and conducted at nightfall. Torchbearers followed by priests wearing surplices and stoles accompanied funerary carts draped in black sheets while chanting the Mass of the Dead. The poet Gabriel Marie Jean Baptiste Legouvé (1804) described the procession as a “shapeless debris-monument to the departed.”
 
 
Wikipedia


LES CATACOMBES DE PARIS - THE CATACOMBS OF PARIS
The Catacombs of Paris lie some 20 meters beneath the south Paris suburb of Montrouge. The town bears little resemblance to the former bucolic royal hunting ground on the Plain of Montrouge. In fact, one must look hard to identify buildings of “old” pre-Haussmann Paris, but they’re there. In fact, you arrive beneath one if you take the Paris Métro at Denfert-Rochereau station, and you must enter one in order to descend into the Catacombs!
 
A good landmark on the street is the bronze statue called the Lion of Belfort within the square, now auto-roundabout. Theatergoers may recognize it as the backdrop at the beginning of the third act of La Bohème by Puccini. General Pierre Philippe Denfert-Rochereau (nicknamed the Lion) achieved fame by courageously fighting against the invading Prussians in 1870 at the city of Belfort in northeast France. Anxious to put a positive spin on his defeat and looking for heroes of the conflict to glorify, French authorities erected the majestic statue in the center of Place Denfert-Rochereau. By the way, the statue was created by Auguste Bartholdi, the father of the Statue of Liberty. 

 
 
 
Place Denfert-Rochereau was previously known as Place d’Enfer or the “Place of Hell”, the street of the infamous collapse of 1774. Rue Denfert-Rochereau was formerly called Rue d'Enfer or the “Street of Hell.” “Denfert” and “d’Enfer” are pronounced exactly the same, a coincidence too perfect for the Paris city hall to ignore when they changed the name - an apparent municipal pun. Interesting sense of humor those French.
 
Here the square and the lion on a 1932 map of Paris. Notice the green space immediately to the west of the Place Denfert-Rochereau. It's the Montparnasse Cemetery. After all cemeteries had been banned in Paris for health concerns, several new cemeteries outside the precincts of the capital replaced all the internal Parisian ones in the early 19th century: Montmartre Cemetery in the north, Père Lachaise Cemetery in the east and Montparnasse Cemetery in the south.  
 
 
View of Barriere d'Enfer along the Wall of the Farmers-General. Note the nearby location of the Lion of Belfort and to the west, the Cemetery of Montparnesse.
Modified from OldMapsofParis.com.
 
 
LA BARRIÈRE D’ENFER – THE GATE OF HELL
Immediately south of the square is the Barrière d’Enfer – the gate built along the Wall of the Farmers-General around the city. Fermiers-Généraux or tax farmers collected octroi at the tollhouses, an unpopular (and highly abused) tax on goods both entering and leaving the city. The two tollhouses on the long-gone wall still remain - four of 62 surviving ones that punctuated the wall built between 1784 and 1791. Actually several walls surrounded Paris between the early Middle Ages to the mid-19th century, the others being for defense rather than tax collection.
 
Here’s an epigram on the octroi that rhymes when recited in French:
 
“To increase its cash
And to shorten our horizon
The Farm judges it necessary
To put Paris in prison”
 
For those interested, you can actually see the outline of the ancient wall on a Metro map of Paris by tracing metro lines 2 and 6, while wide boulevards replace the former fortifications. Also, the Rotunda at Parc Monceau on the north side of Paris on the Right Bank – originally called Barrière de Chartres - is an elegant tollhouse of the few that remain on the barrier wall.
 
 
 
 
Back at Denfert-Rochereau, two neo-classical tollhouses on the long-gone wall still remain. The easternmost building (right in the photo) is reserved for the Inspector General of the Quarries and is the site of entry into the catacombs – our entry into hell. The westernmost building (on the left) houses offices of the Directorate of Roads and Transport. Notice the Lion of Belfort on a pedestal in the center of the public square.
 
 
 
 
In spite of the nightly rituals of interment, the Catacombs were unknown to the public at large until 1810 when the second General Quarry Inspector, Louis-Étienne François Héricart-Ferrand, issued the first brochure that advertised their presence and began drawing curious Parisians into their depths. Prestigious figures that followed included Francis I of Austria in 1814 and Napoleon III and son in 1860. Today, the Catacombs have become a major tourist attraction and is managed by the City of Paris Cultural Affairs Division in association with the Carnavalet History of Paris Museum.

During the 1830’s to 1840’s, excursions were not limited to just the Ossuary and led by mine overseers “who guided them as struck their fancy; inevitable abuses occurred, the quarry galleries as well as the ossuary were damaged by unscrupulous people and visitor lost their way.” (Emile Gerards in Paris Souterrain, 1991).
 
OUR DESCENT INTO THE CATACOMBS
We arrived at the east pavilion of the Catacombs well before the opening time of 10 AM and found a line already forming at the entrance. Both Parisians and tourists alike want to be amongst the first 200 visitors allowed in, and we were no exception.
 
To enrich our experience, since tours are delivered in French, we arranged for an English-speaking guide and most affable fellow from Ireland (although audio-guides are available French, English and Spanish). He was extremely knowledgeable about both French and world history, and spoke four or five languages, so he was able to translate the 18th century signage in the Catacombs.
 
After purchasing our tickets, we descended a tight, spiral staircase of 130 steps into a dimly lit gallery 20 meters below street level – equivalent to a five-story building.
 




The entire tour covers a distance of about two kilometers and winds through a dimly lit labyrinth of galleries and interconnecting tunnels beneath the streets of Montrouge. The official brochure states that the average duration is 45 minutes, but we easily took twice that. There is a constant temperature of 14º C (57º F).

Be forewarned, as there are no toilet or cloakroom facilities within the Catacombs. Lastly, as stated by the official Catacombs Visitor's Guide, the tour is unsuitable for people with heart or respiratory problems, those individuals of a “nervous disposition” or claustrophobic, and young children. There is no disabled access to the Catacombs. The experience is quite macabre to those unaccustomed but incredibly fascinating in regards to Parisian history, geology and paleontology.


La Visite aux Catacombes, Aquarelle, 1804-1814, Musee Carnavalet
 
Visite aux Catacombes
Reproduction d'une gravure anglaise, 1822, Carte postale, vers 1900, Collection Roger-Viollet
 
 
LA MER À PARIS - THE SEA IN PARIS
Between street level and the Catacombs, visitors travel back to the Lutetian age. At the bottom of the spiral staircase and before entering the Catacombs proper, visitors are guided to an exhibition entitled “The Sea in Paris – 45 Million Years Ago,” which ends December 31, 2014. The new installation “highlights a little known aspect of the Catacombs – their geological heritage, a real treasure-house in the subsoil of the capital.” (Of course you can read it all in my post Part I here).
 
A series of murals in both French and English takes you on the “journey through space and time” with paleographic maps, chronological profiles, photographs, drawings and engravings that beautifully demonstrate the evolution of the Paris Basin and the Lutetian Sea. In addition, there’s a detailed description of the Left Bank’s limestone quarries and the circumstances that led to their repurposing as an ossuary.
 
 
One of many geologic maps and cross-sections on display that depict the tectonic and geologic evolution of the Paris Basin and the region of Paris. My red arrows identify the underground limestone quarries (calcaire carriers souterraines de calcaire) of the Left Bank, south of the River Seine and the open air Roman quarries carrieres a ciel ouvert), also on the Left Bank, along the River Bievre.
 
After departing from the exhibition, the tour continues through a long interconnecting corridor. It seemed like a long distance to the Ossuary within the narrow walls and low ceilings.
 
 
Corridor leading to the Ossuary portion of the Catacombs
 
  
LES SCULPTURES DE PORT-MAHON - THE SCULPTURES OF PORT MAHON 
The Catacombs is filled with many curiosities, not all of which are on display. Perhaps the most unique and popular is the sculpture created in 1782 by Beauséjour Décure, a discharged soldier who had been enrolled in the army of Richelieu during the re-conquest of Minorque. Although only a few details of his life are known, once discharged he worked in the quarries. During breaks, for five years Décure chiseled a replica of Port-Mahon, the principal port of Minorque, out of limestone. Wanting to make his creation more accessible, he was killed by a cave-in while opening an access stairway to his model. Currently, the sculpture is not included in the protective measures of the Ossuary and is threatened by a real estate project overhead. "C'est la vie."
 
 
 
 

LE BAIN DE PIEDS DES CARRIERS - THE QUARRYMEN'S FOOTBATH
The first geological drilling undertaken in Paris (actually under Paris) was carried out by Héricart de Thury in 1814. Dubbed "The Quarrymen's Footbath", the well contains crystal clear groundwater that has percolated into the drilled-depression. The only way to detect its presence is to step into it. One can only guess the mischievous pranks guides carrying candles and torches must have had with their tours. The water was subsequently used by quarry workers to mix cement required for the Catacombs.

Limestone is more or less finely porous and permeable to water. At depth - from a few centimeters to several hundred meters - and depending on the series of geological strata and the relief, the rocks are saturated with water. This forms a series of superimposed phreatic zones or aquifers, separated by impermeable argillaceous (clayey) rocks. The water table represents the first phreatic zone to be reached when a well is dug such as the Quarryman's Footbath. Its surface fluctuates with the whim of the rain or even the nearest river. By the way, the principle of artesian wells was demonstrated in 1828 by Héricart de Thury and later applied in the drilling of the Grenelle well in the 15th arrondissement of Paris. 


Bains de Pieds des Carrieres, Catacombs Brochure, DAC/Ch. Fouin


THE EMPIRE OF DEATH
You’ve officially entered the Municipal Ossuary having passed beneath the engraved, limestone lintel that declares “Stop! This is the empire of death”. Of course, tens of thousands of visitors every year are hardly dissuaded by the ominous warning. In actuality, this is the “new” entrance, the original being at the end of the ossuary. Visits to the ossuary begin with the most recent bone transfers.

The limestone quarries have been closed to the public since 1955, but the Catacombs have remained open. At the time that Guillaumot was strengthening the tunnels beneath Paris, King Louis was closing the overcrowded cemeteries. The exhumations went on for years - long after the King lost his head in the French Revelation in 1793 - until all the bodies had been reinterred in a new realm – this, the Empire of the Dead.




The black tar line on the ceiling was traced as a path to follow by candlelight to prevent 19th century visitors from losing their way in the maze of galleries. An example of how easy it is to get lost is told by the tale of the porter Philibert Aspairta, who entered the quarry alone in 1793 and lost his way. He was found by a survey crew 11 years later and given a proper burial where he had been discovered.

In the words of L.F. Hivert in 1860:

“We etched a broad black line commencing at the base of the staircase and meandering all the way through this vast labyrinth. A stray visitor, provided he has light, need only follow this Ariadne’s thread to find the door. From place to place, the line bears an arrow pointing towards the exit door, as the flow of a river is marked on a map.”

Immediately within the entrance to the ossuary is a stele (funerary monument) dated 1810 that commemorates the establishment of the Catacombs. It was moved from the original entrance when the ossuary was expanded.

 
 
 
“Catacombes established by order of Monsieur Thiroux de Crosne, Lt. General of Police, and by Monsieur Guillaumot, Inspector General of Quarries, 1786. Restored and improved by order of Monsieur Frochot, Secretary of State, Chief of the Department of the Seine, by Monsieur Hericart de Thury, Chief Mining Engineer, Inspector General of Quarries, 1810.”
 
BONE STACKING
In the first years, the Catacombs was a haphazard repository, but renovations in 1810 transformed the underground ossuary into the visible mausoleum (and tourist attraction) that it is today. Skulls and femurs were stacked in repeating patterns in total anonymity, while funerary decorations such as monumental tablets, archways bearing inscriptions, warnings and even poetic verse were installed to complement the walls of bones.
 
 
Wikipedia
 
WALL AFTER WALL LINED WITH BONES
Although some sections of the Ossuary contain a haphazard array of bones, the tour only reveals those neatly arranged in cranium-studded friezes of skulls (maxillae only, no mandibles or teeth!), femurs and tibias. Both macabre and somehow strangely romantic, I could only imagine what fantastic tales of life in Paris the speechless skulls would tell - having lived during reigns of King Louis XV and XVI, the French Revolution, and the Reign of Terror and its infamous guillotine.
 
 
 
 
The City of Light's 12 million residents live in the world above, while below the streets in the Empire of Death 6 million remain at rest. There are many signs within the Ossuary. Some record the street on the surface above, often with names that since have been changed. Some document the date of consolidation, while others merely record the depth below the surface in both feet and meters. The cemetery of origin from which the bones originated and the date of transfer were carefully recorded. Most of the cemetery-names are long-gone and long-forgotten - with the exception of the most famous and infamous - Saint-Innocents.
 
 
 
“Bones of the Cemetery of the Innocents Deposited on July 2, 1809”
 

 
 
"Bones of the Church and the Cloister of the White Coats June 22, 1804"
 
Many of the ceilings (note also above photo) display tiny stalactites as water percolates through the limestone overburden. The incessant dripping over time deposits calcium carbonate in the same manner as seen in karstic limestone caverns. 
 
 
Tiny stalactites forming on the ceiling of the Catacombs
 
 
The ever-present tar-line on the ceiling guides our way. The spiral markings are algal laminations on the floor of the Lutetian Sea, seen from the underside.
 
 
 
 
 
Some of the 18th century signage records overlying collapse structures. This one documents the location of a fontis-sinkhole and the initial "J" of quarries inspector Chrétien-Auguste Juncker in 1842.
 
 
 
 
MEMORIAE MAJORUM - IN MEMORY OF THE ANCESTORS
At the end of the ossuary portion of the Catacombs, that once served as an entrance door, is a low portal with an engraved lintel in Latin - MEMORIAE MAJORUM – “in memory of the ancestors.” The reverse side of the lintel states “Wherever you go, shadowlike death will follow.”




The Catacombs of Paris reminded me of a 17th century Capuchin crypt in Rome beneath the church of Santa Maria della Concezione dei Cappuccini that I had visited years ago. It contains the remains of a mere 3,700 skeletons by Parisian standards that were also transferred and artistically arranged in a similar manner (although many skeletons were clothed and others made into decorative chandeliers). A placard there warns the onlooker in five languages:
 
“What you are now we used to be; what we are now you will be.”
 
LA CLOCHE DE FONTIS – THE SUBSIDENCE BELL
The next corridor leads to a gallery consisting of a number of subsidence sinkholes (fontis) consolidated between 1874 and 1875, three of which are over ten meters deep. The rubble that had collapsed from the ceiling has been excavated and allows the viewer to observe its bell-shaped structure.




Rather than cover the walls with hand-stacked masonry-retainers, some subsidence structures were simply consolidated with sprayed cement. The fontis seen below was reinforced with an arch, whereas others were reinforced with an internal shell of masonry. The stratigraphic layers can be viewed in cross section as if seen from within a bell. The colored lines were added to help delineate the strata – an embellishment that I could do without.

In all, it’s a quite remarkable catastrophic collapse-structure that can be viewed from within and an incredible display of quarry history. One must remember that these very subsidence bells threaten the lives of Parisians on the surface, although most everyone goes about their daily lives with total nonchalance.


Cloche de fontis aux Catacombes


Many, if not most, of the "bell-holes" are located beneath critical structures on the surface such as buildings, busy street and Metro stations. The apex of this fontis contains the date "1875" written in mirror-image.
 
 
 
 
 
TECTONICS, GEOLOGY AND PALEONTOLOGY ON DISPLAY
At three various locations within the Catacombs, the story of the tectonic and geological evolution of the Paris Basin and the Lutetian Sea is beautifully displayed on murals in understandable terms. During the Lutetian epoch of the Eocene, centered about 45 million years ago, the waters of the nascent Atlantic Ocean repeatedly flooded the continental shelf of Europe and its many basins. The Anglo-Paris Basin received sediments of sand, clay and limestone.
 
One such layer, a limey sludge, hardened with the passage of time until it became the fine, even limestone known as Banc de Saint-Leu, which is highly sought after for cutting into building stone. And within the epicontinental basin, a shallow, sub-tropical sea much like the present-day southern Mediterranean was teeming with marine life - worms, gastropods, bivalves, corals, urchins, fish, nautiloids, crabs, sharks, etc.
 
 
Plaster cast of Campanile giganteum, an exceptionally large marine gastropod from the Eocene epoch of the Paris Basin, was on display within the Catacombs
 
Nummulites laevigatus, a foraminifera that left a fossilized shell that looked like a "liard" (a small Medieval coin) formed a meter-thick layer called pierre a liards or liard stones.
 
FAMOUS NATURALISTS OF THE LUTETIAN
By the end of the lower Lutetian, the sea had reached the site of present-day Paris. With its final recession, the lagoonal and mangrove landscape gave way to an arboreal savanna rich with a terrestrial flora and fauna. The skeletons of extinct early mammals - such as the pre-ice age mammal Palaeotherium - were excavated from the gypsum mines of Montmartre on the Right Bank and studied by the French naturalist Baron Georges Cuvier, founder of the science of comparative anatomy and vertebrate paleontology. Cuvier was not ready to suggest that animals had evolved through time, but he did arrive at the inescapable conclusion that the fossils were the remains of animals long-extinct, implying that God had allowed some of his creations to vanish. 
 
 
This commemorative plaque is on the wall of Louise-Michel square at the northern end of the rue Ronsard, which was the entrance to the quarries of Montmartre that are beneath the Basilica of Sacré Coeur. It was here that Cuvier discovered mammalian fossils in 1798.
 
Cuvier also noticed that the Lutetian fossils of the Paris Basin differed with each strata. Working with the mollusk expert Alexandre Brongniart, Cuvier was able to identify the basin's different layers based on their distinctive fossils. 
 
 
Cuvier's and Brongniart's joint venture in delineating the stratigraphy of Paris in 1832
 
 
Cuvier avoided conflict with the powerful theologians of his time in his interpretation that the extinct animals were victims of Noah's biblical flood, and in so doing, became an early proponent of catastrophism in geology (past dramatic events can explain changes in geological features and the extinction of species). The two established the first geologic maps and cross-sections in France and Continental Europe including the Paris Basin.
 
 
This 1810 copperplate, colored geologic map of the environs of Paris (arrow) by Cuvier and Brongniart was established in part by identifying fossils in various sedimentary strata. Limestone is pink; gypsum is blue; marine marls are yellow; green areas are freshwater terrain. William Smith's many geologic maps of England were also being generated by this time. 

 
EXITING THE CATACOMBS
One must depart from the Catacombs in the same manner as the arrival by ascending a narrow, spiral staircase - this time with only 83 steps - from a depth of 54 feet from the street. Unlike the entrance staircase, the exit dates back to the origins of the Catacombs. The exit is at 36 Rue Rémy-Dumoncel, still within the working-class suburb of Petit-Montrouge.
 
We have completed a subterranean journey of 1,500 meters, of which 600 meters proceeded between the walls of bones of the Ossuary. In spite of the distance, which seemed longer due to the narrow tunnels and absence of a visual horizon, we only experienced a very small section of the Catacombs and a tiny section of the underground limestone quarries that lie beneath the Left Bank!
 

Our catacombic, underground journey began at the Barriere Denfert-Rochereau (upper arrow)
and followed a winding path to 36 Rue Rémy-Dumoncel (bottom arrow). 
Google Earth  


As if 6 million skeletons wasn't enough, a subtle reminder of the tenuous grip on life that we all possess rests strategically on the wall immediately at the top of the arduous stair-climb to the street.
 
 
 
 
Our unceremonious, eye-squinting exit from the Catacombs was from an unmarked, nondescript stone-structure on a quiet side street of Petit-Montrouge. Across the street (to the left outside the image) is a fantastic bookstore with numerous titles on the quarries and the Catacombs, however, most were written only in French. 
 
 
 
 
A REMARKABLE TRANSITION FROM CEMETERY TO PUBLIC SQUARE
It's been over 225 years since the King's edict to close the Cemetery of Saint-Innocents was issued. Since then, much of Paris's landscape has changed, most notably during the radical urbanization program of Napoléon III and his Prefect of the Seine Georges Eugene Haussmann in the 19th century. The limestone quarries and the overcrowded, center-city cemeteries have closed, and their bones have been moved to the Municipal Ossuaries called the Catacombs.
 
There’s little on the modern landscape of Paris to remind us of the intolerable conditions that existed at Saint-Innocents during the 18th century, that is, unless you know where to look. Following the closure of the Cemetery of Saint Innocents in 1786, the Church of Saint Innocents was destroyed as the bodies were being transferred in the night to their haven of peace within the Catacombs. The Fountain of the Nymphs, which had been erected against the wall of the church in 1549 and was also scheduled for destruction, was dismantled and rebuilt in the center of the new square and marketplace, Place Joachim de Bellay. A painting by Hoffbauer in 1850 depicted the transformation of the cemetery into a bustling marketplace with stalls and umbrellas.
 
 
The square and market of Place Joachim de Bellay with the Fountain of Innocents in 1850
Theodor Josef Hubert Hoffbauer (1839-1922), Public Domain.
 
Today, after several embellishments that included a larger pedestal and central fountain with a series of cascading basins , the newly-titled Fountain of the Innocents is within the square but located in a small corner of the original cemetery. The proximity of the Saint-Innocents Cemetery to the original marketplace of Les Halles is preserved in the square’s proximity to the Forum des Halles, a modern underground market and shopping area reconstructed in 1971 from the original market.
 
 
Modified from Wikipedia
 
A portion of the original, bone-containing charnel house still stands along the border of the square and houses a popular pizza joint. The square is a quiet and peaceful place with Parisians reading and kids playing ball. What indescribable sights the monument has seen!
 
 
The Fountain of the Innocents within Place Joachim de Bellay
Photograph by Janet Penn. www.janetpennphotography.
 
 
THE QUARRRIES AND CATACOMBS OF PARIS TODAY
Today, quarry inspections are still conducted by the Inspection des Carrieres, established in 1777. This 20th century manhole cover on the Left Bank testifies that the IDC is still on the job. The techniques of quarry reinforcement have changed. They are no longer consolidated with masonry work but by drilling and injecting backfill materials.
 
 
 
 
Ironically, the savior of the city - Charles Axel Guillaumot - never had a street, monument or plaza named after him. What’s more, his remains anonymously joined the millions of bones and skulls in the Catacombs, the ossuary repository that he had created to clean up the cemetery of the Saint Innocents. Another point of interest, Guillaumot was imprisoned in 1791 during the French Revolution and removed from his position because of his appointment by the King. Recognizing his importance to the city, he escaped the guillotine and was returned to his position in 1795.
 
As for the River Bièvre, the tributary along which Romans exploited its banks for limestone, it flows freely in the outskirts of Paris and still empties into the Seine but is now almost totally submerged and diverted within vaults and tunnels under the buildings and streets of the Left Bank. The Bièvre was heavily polluted by chemicals from the tanneries that lined it in the 19th century. Local residents have called for the rehabilitation and unearthing of the Bièvre or at least a portion of it on the grounds of the Muséum d'Histoire Naturelle.
 
 
A "freely-flowing" Bievre River in the 5th arrondissement c. 1862 taken by the government commissioned photographer Charles Marville 
Wikipedia and the Museum of Art, The Horace W. Goldsmith Foundation Fund

 
These days, in addition to becoming a city-promoted tourist attraction, the Catacombs have also become a parallel, sub-universe populated by "cataphiles" - illegal subterranean explorers and young, bohemian Parisians who use the underground galleries and tunnels as party venues and places to hang out and paint decorative murals. Secret entrances exist throughout the Left Bank of Paris via sewers, the Metro and manhole covers.
 
 
From National Geographic
 
In spite of sophisticated mapping, detailed inspections and modern quarry consolidations, catastrophic collapses still occur on the Left Bank as seen below recently. Notice the Lutetian stratigraphy within the fontis! On average, seven collapses occur a year in Paris, in spite of intensive efforts to stabilize the underground quarries. A collapse in 1966, triggered by heavy rains, opened a chasm in the street that swallowed six streets and part of a soccer stadium. Twenty-one people were killed, 273 were left roofless and 23 buildings were completely destroyed. In 2003, an entire school building collapsed into Metro tunnels compromised by underground excavations. Anxious eyes continue to watch the streets and people of Paris.
 
 
 
 
Early warning of collapse is possible with remote Interferometric Synthetic Aperature Radar (InSAR) emitted from satellites and aircraft. The process can spatially monitor small, slow-rate vertical ground deformations seen with subsidence, uplift, landslides, volcanoes and earthquakes and generate maps of surface deformation. InSAR has been used successfully in major cities such as Paris, and has become a valuable tool for land-use planning and natural as well as anthropogenic risk assessment.
 
 
Mean Amplitude Image of Paris with Satellite Radar Interferometry Analysis
Arrow “a” indicates a mean subsidence event of -3mm/yr in the Grand Palais area during the period 1992-2000. Arrow “b” corresponds to the Saint-Lazare area studied in 2000 and 2002. Arrow “c” corresponds to a subsidence of -2mm/yr around the Montmartre area.

Modified from earth.esa.int/psic4/background.html

 Color-coded maps of surface deformation can be generated over time.
 
 
Set of Phase Screens of Paris
The various colors represent levels of deformation.
From asprs.org
 
 
IN CONCLUSION
My recent visit to Paris served to further reinforce the theme stated in the masthead of my blog that “Geology is all around us, scarcely thought of as we go about our lives. Yet, it affects everything we do as a civilization, as a society and as individuals.”
 
The Lutetian deposits of gypsum on Paris’s Right Bank beneath the hills of Montmartre and Belleville provided plaster of Paris for the city and the world. The Left Bank deposits of limestone built the city, and the quarries that honeycombed its depths provided a necropolis for the countless millions of Parisians buried there. 
 
ADDENDUM
Upon our ascent from the Catacombs, my wife and I found ourselves within a stylishly quaint neighborhood of Petit-Montrouge. What a contrast from where we had been amongst the Empire of the Dead and into the Realm of the Living. In a matter of minutes we had traveled from pre-17th century quarries through an 18th century ossuary, into a 19th century fontis excavation, up a set of 19th century steps, and out of a 20th century building to the 21st century. I took out my Smartphone, launched the App for Zagats and found a perfect bistro for lunch for the two of us just down the boulevard. La joie de vivre!
 
VERY INFORMED PRINTED SOURCES OF INFORMATION AVAILABLE FROM THE CATACOMBS BOOKSTORE AND ON-LINE
Atlas du Paris Souterrain under the direction of Alain Clement and Gilles Thomas, 2001. A fantastic, thorough and entertaining presentation in French with wonderful photographs.
Paris Souterrain by Emmanuel Gaffard, 2007.
The Catacombs of Paris by Gilles Thomas, 2011. Another thorough presentation.
 
 
WEBSITES OF INTEREST - ALL IN FRENCH
 
“Behind every man now alive stand thirty ghosts, for that is the ratio
by which the dead outnumber the living. Since the dawn of time,
roughly a hundred billion human beings have walked the planet Earth."
 
Arthur C. Clarke