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. While barely appearing to change from day to day, it works to alter the course of evolution. Preserving a record of creatures and landscapes both ancient and forgotten, the story of our past is written in stone and waiting to be read. I offer a view of how I see our world and its inhabitants, both past and present, as seen through my lens.
Native Swamp Candles (Lysimachia terrestris) or Yellow Loosestrife, a member of the Primrose family, await visitors to the bog on its swampy periphery. The flowers are star-shaped with five yellow petals displaying two red dots their bases. Together they form a circle of ten red dots in the center of each flower.
WHAT IS THE PHILBRICK-CRICENTI BOG?
The bog is a poorly-drained (soil-saturated), acidic (decomposing), nutrient-poor (receives no organic runoff), kettle-hole (glacially-derived) wetland that receives its precipitation largely from rain rather than from an inlet-stream or neighboring-runoff. It is covered with a soft, interwoven, spongy mat of Sphagnum moss, sedge, and dwarf heath shrubs that literally floats on the surface. Beneath this “buoyant carpet of vegetation” are the partially, decomposed remains of waterlogged, dead plant material called peat. Essentially, Sphagnum moss and other plantlife grow at the surface and die at the bottom contributing to the formation of peat. The plant communities that inhabit the waterlogged realm of the bog are capable of tolerating its unique and demanding environmental conditions by exhibiting an enormous capacity for adaptation and diversification.
To visit the bog’s buoyant interior and not disturb the fragile plantlife underfoot, one must walk upon a mile-long network of trails on wooden planks. The planks provide a safe path over the floating mat of tundra plants. It’s an amazing experience!
A plank of boards leads from the peripheral wooded region to the center of the bog. Notice the magenta flowers of the Calopogon orchid scattered throughout the floating mat of Sphagnum and sedge.
WHAT’S AN ORCHID?
Orchids are an extremely diverse family of plants morphologically that occur in a virtual rainbow of colors. They get their name from the Greek word for testicle that refers to the appearance of their underground tubercles (which not all orchids possess). Orchids are actually the largest family of flowering plants having twice the number of species as birds and four times the number of mammals. Its flower is a very unique reproductive structure that allows both pollination and seed formation.
All orchids are members of a flowering group (angiosperm) of plants called monocots (meaning one leaf in the embryonic leaf-stage) versus dicots (with two leaves). Monocots (such as palms and the grass family of plants like rice, corn, wheat) include many plants cultivated for their blooms such as lilies, daffodils, irises, tulips, and of course orchids. Examples of dicots include roses, magnolias, tomatoes, peanuts, and trees such as oak and maple. The orchid’s flower, being a monocot, is trimerous, meaning the flower has petal-parts that are in multiples of three.
Surprisingly, orchids occur in almost every habitat with the exception of glaciers and deserts, but are even found above the Arctic Circle. The greatest majority are found in the tropics with the world’s richest concentration of orchid varieties found in the Himalayan region of Nepal.
Orchid Distribution of Growth: Red band = terrestrial and epiphytic (grow in trees) Yellow band = terrestrial orchids only (From Dressler, 1981)
CO-EVOLUTION AND CROSS-POLLINATION
Monocots evolved early in the history of flowering plants during the Early Cretaceous, and certainly before dicots. The orchid is thought to have evolved from a lily-like ancestor. Flowering plants co-evolved with insects. Flowers diversified with vivid colors and fragrances in order to attract pollinators. The orchid’s flower is specialized in order to attract specific insects in order to increase the chances of pollination.
Cross-pollination is a beneficial strategy for long-term survival. It provides variation in populations (speciation) for flexibility in the face of environmental change. Thus, “orchids have formed an alliance with insects” (Stephen Jay Gould). They evolved an astonishing variety of “contrivances” (Charles Darwin) to attract insects such as the shape, color and fragrance of the flower’s sexual organs. This serves to insure that sticky pollen adheres to the visitor and ensures that pollen contacts the female parts of the next orchid by the insect, thereby exchanging genetic information (ergo cross-pollination).
Pollintors, by the way, don't just include insects such as bees. Many orchids have established pollinator relationships with flies, gnats, moths, butterflies, hummingbirds, and even bats!
A LITTLE ORCHID ANATOMY LESSON TO ENHANCE OUR APPRECIATION The most unique aspect of orchids are their exotic flowers which have many structural variations. As with most insect-pollinated flowers, the orchid’s flowers are brightly colored, possess a strong, sweet fragrance, and produce an attractive nectar (the pollinator’s reward). Some orchids have single flowers, but most have an inflorescence (arrangement) with a shoot bearing many flowers.
Being a monocot, the orchid’s flower possesses two whorls (spirals) of six petals (in multiples of three). The outer whorl has three sepals, which in most flowers are green. In orchids, the sepals are usually similar to the petals (orchid’s sepals are then called tepals). The sepals are connected to the stem and protect the flower in bud. The inner whorl has three petals (usually the showy part of any flower), but one particular petal called the labellum (lip) is distinctly modified and enlarged. The orchid’s labellum provides a landing-platform for pollinators and is usually on the lower part of the flower (resupinate). All aspects of the orchid flower's anatomy is geared toward insect attraction, staying awhile, and cross-pollinating!
These morphological features of the orchid's flower can be seen in the Calopogon below which was in full bloom at the bog. Dazzling!
The "Grass pink’s" whorl of three outer sepals and three inner petals can easily be seen.
The labellum is a modified-petal to enhance the prospects of cross-pollination and is uniquely
situated at the top (non-resupinate) of the Grass pink’s flowery display rather than the bottom. The prominent column containing the plant’s combined, reproductive organs is seen at the center of the flower.
ORCHIDS HAVE EXTREMELY ATTRACTIVE SEXUAL ORGANS
Stamens are the male reproductive organs of all flowers with the pollen-containing anther at the end of a stalk or filament. The female reproductive part of a flower is called the carpel. It includes the stigma located at the top of a style (where pollen germination occurs) and the ovary (at the base of the carpel). Germinated-pollen produces a pollen-tube that grows down the style to get to the ovary, which becomes the fruit (a ripened ovary) and contains the seeds.
A typical flower illustrating multiple male stamens surrounding a centrally-located female carpel.
Notice the green sepals and the colorful petals.
(Modified from kvhigh.com)
In the orchid both sex organs are combined into one unique, reproductive organ called the column (gynandrium), which is the distinguishing character of the orchid family. The tip of the column holds the male anther and its mass of pollen, and below it is the female stigma, that receives the pollen upon pollination. Below the stigma is the ovary, which is actually below the flower and within the stem of the plant.
A typical orchid illustrating three sepals and three petals. The reproductive organs are combined into one structure called the column that is situated on the labellum. The labellum is a landing-platform provided for pollinators. The ovary is contained within a portion of the stem rather than the carpel. (From nybg.com)
SEXUAL EXPLOITATION, DECEPTION AND FALSE PROMISES
The beautiful magenta-flowered Calopogon tuberosus (Greek for “beautiful beard”) is also known as “Grass pink.” The beard refers to the cluster of yellow-hairs on the labellum which sits at the top of the flower (non-resupinate) rather than the customary bottom position (resupinate). The Calopogon is a hardy orchid despite its delicate beauty and loves the acidic-soil of the bog. Its presence in the bog is an indication of a high quality and healthy, hydrologic system.
Amazingly, the hairs on the lip of the Calopogon act as a “pseudo-pollen”, a deceptive lure to pollinators.
Naïve bumblebees, expecting a reward of nectar, land on the hairs. The hinged labellum then swings down under the bee’s weight and positions the bee on the orchid’s sexual column, where pollen can be placed
on the bees back for transport to another flower. To add injury to the insult of no reward,
the bee must then crawl out of the closed flower. The Calopogon is further deceptive
by mimicking the appearance of another nectar-bearing flower.
ENDANGERED, THREATENED AND SO VULNERABLE
The Platanthera (Habenaria) blephariglottis or “White-fringed” orchid is variably considered to be endangered, threatened or vulnerable in many regions. Its "Orange-fringed" cousin grew by the thousands in Rhode Island and around New York City, but urban sprawl made them a memory. The Platanthera loves the wet soil found in bogs, and the moist banks of lakes, rivers and streams. It has lateral sepals that bend downward and outward. The plant has many white to cream-colored flowers which are pollinated by butterflies and moths.
The labellum of the Platanthera is fringed and has a slender, elongated spur.
In the first week of July, this multi-flowered Platanthera is perhaps a week away from full bloom.
Its flowers are arranged on a stem in an inflorescence with a close-cluster of flowers.
In the sunniest part of the bog, the White-fringed orchids are closer to full bloom.
In venturing out onto the bog I had no idea of the varied, delicate, exotic and beautiful orchids that grew there. In fact, I had little conception of the dynamics and complexity of the entire biome of the bog. For me, the Philbrick-Cricenti bog continues to be a source of stunning beauty, new wonders and surprises at every change of season.
A roadcut is an excavation into a hill or mountain created by civil engineers, usually through blasting, for the purposes of building a road. Fortunately, for urban dwellers, such as myself, living in a region where structure is not well exposed, a great deal of geology is visible through roadcuts. This is especially true in the densely-populated, paved-over, heavily-vegetated, highly-eroded and glacially-scoured world of Greater Boston.
Roadcut exposing the dark gray Medford Dike, as it intrudes its way out from the bowels of Interstate 93 South
In Annals of the Former World, John McPhee, a Pulitzer Prize winner, wrote “The roadcut is a portal, a fragment of a regional story, a proscenium arch that leads imagination into the earth and through the surrounding terrane. In the rock itself are the essential clues to the scenes in which the rock began to form. Unfortunately, highway departments tend to obscure such scenes. They scatter seed wherever they think it will grow. They “hair over everything”---as geologists around the country will typically complain."
Personally, when I see a roadcut, it’s like seeing the Holy Grail. It’s a chance to view the landscape of the ancient past. It's an opportunity to "read the rocks." Roadcuts aren't to be missed. Take a ride with a geologist, and you'll see what I mean. Nothing else matters, with my car lurching and weaving, and my wife admonishing me with “Keep your eyes on the road!” I’ve only got one good shot at seeing that roadcut, as we go careening by on the highway. Better make it good!
McPhee goes on to say, “Without roadcuts, all you could do is drill a hole, or find natural streamcuts, which are few and far between.” Fortunately, living in New England, roadcuts are relatively abundant. McPhee continues, “A roadcut is to a geologist, as a stethoscope is to a doctor. An X-ray to a dentist (he struck home on that note). The Rosetta Stone to an Egyptologist. A twenty dollar bill to a hungry man.” Anyway, you get the point.
Recently, I drove past a “famous” local roadcut. It contained the Medford Dike, a few miles north of Boston. The dike qualifies as a famous rock formation in New England, certainly amongst geologists. The only other geologically well-known structure that comes to mind (and I’m sure there are others) is the “Old Man of the Mountains” in New Hampshire, a granite rock-face (literally) that was decapitated by the forces of erosion and mass wasting in 2003. Except that the Old Man is (or was) known more for historical and touristic aspects than those strictly geological.
Losing-face doesn’t prevent the State of New Hampshire from missing the old guy. He’s still on their license plates.
Anyway, back to the Medford Dike. I must admit that I knew the roadcut was coming. I was fully prepared and driving alone. The dike is best seen from the southbound lane of Interstate 93 at mile marker 23.6. The speed limit is 65 mph, but everyone does 80. Enough time for one good shot! Heading south, I had my passenger window rolled down, camera in hand, shutter speed set to 1/1000, and my left hand on the wheel. No one to admonish me on this one!
The 375 foot-wide Medford Dike is a volcanic, “feeder” comprised of biotite gabbro and dated at about 190 million years of age. Its magma intrudes the Lynn Volcanic rocks and is one of 1,000 to 2,000 basaltic dikes that intruded rocks of the Avalon terrane in the vicinity of eastern Massachusetts. This was the time when the newly-formed Atlantic Ocean began to spread at the consequence of the supercontinent of Pangaea, which was rifting apart.
Geologic map of the Pine Hill area in Medford, Massachusetts.
The Medford Dike (Jd) can be seen trending northeasterly. Note the swarms of other intrusive dikes in the vicinity and the transection of the dike with I-93.
(From Wilson, 1901)
About 230 million years ago in the Middle to Late Triassic, Pangaea began to initially fragment at the southeastern portion of North America. Pangaea began to split apart along deep-seated faults. The main zone developed into the North Atlantic Ocean basin between Africa and North America, but numerous major rifts also formed along the edge of the newly-forming circum-Atlantic continents. Along the east coast of North America (then south-facing), a complex rift-system developed with many northerly-trending basins, some onshore, and some now submerged beneath the ocean or buried on land.
Seen here in the earliest Jurassic, Pangaea has initiated its break up, beginning with the North Atlantic.
Around 201 Ma, the time of the Medford Dike, magmatic injections in the form of a giant dike swarm began somewhat synchronously with the progression of rifting to the north-northeast. In so doing, the Triassic-Jurassic rift system in eastern North America was formed. The sedimentary fill and lava flows of the rift basins, fed by such dikes as the Medford, are collectively known as the Newark Supergroup and belong to the multi-continental rift system of the Central Atlantic Margin (CAM) system.
This illustration shows the formation of dikes and sills, intrusive rocks containing coarse-grained, mafic rocks such as gabbro. The extrusive flows at the surface fed by the feeder-system have long since eroded away.
(Modified from the University of Toledo’s Website)
The dikes and basins of the rift system are indicative of stretching of the continental crust at the time that the Atlantic Ocean was beginning to form and signaled the dispersal of the continents that we know today throughout the globe. Eventually, North America and South America separated from Africa, creating the Atlantic Ocean by beginning to rift apart initially in the North Atlantic basin.
The breakup of Pangaea has initiated in this 195 million year perspective. The arrows indicate the drifting that is occurring between the continents of North America and Africa that are about to form. The region of Greater Boston is located within the ellipse. As the young Atlantic Ocean began to form, numerous rift basins developed parallel to the rift. This was a time of subsidence and sedimentation within the rift basins, and flood basalts. The extrusive flows were fed to the surface by a massive, intrusive magmatic system with "feeders" such as the Medford Dike. (Modified from Ron Blakey, Colorado Plateau Geosystems, Inc. and through the generosity of Wayne Ranney)
Before rifting of Pangaea took place, Boston was located far inland, within the epicenter of the huge Pangaean supercontinent. The only reason that Boston is on the Atlantic seaboard today is because rifting initiated right near it.
CAM rift basins (black) of the circum-North Atlantic shown on an early pre-drift reconstruction.
So, when you drive by the Medford Dike, let it be a reminder of the time when Pangaea was about to break up, and give birth to the Atlantic Ocean, dispersing the contemporary continents throughout the globe. The Medford Dike is also easily visible (and more safely) by hiking the Pine Hill area in the town of Medford. There, you can observe the dike as part of the bedrock rather than as a roadcut. If you choose to photograph it from I-93 South, like me, remember to “Keep your eyes on the road!”