Urban Geology - Part I: The Filling In of Boston's Back Bay

"Well, I love that dirty water.
Oh, Boston, you're my home"
The Standells, 1965

PROLOGUE
Some 600 million years ago, a chain of volcanic arc-islands and related arc-basins rifted from the northern margin of the massive South Hemispheric continent of Gondwana. In particular, the Avalonian arc and Boston Basin initiated a transequatorial tectonic journey across a closing Iapetus Ocean and welded to Laurentia, the North American craton. Following Gondwana's amalgamation, the microterrane and basin became landlocked within the Appalachian orogen of Pangaea in the late Paleozoic. They achieved a seaside locale in eastern Massachusetts only after the supercontinent's fragmentation and initiation of Atlantic seafloor spreading in the Mesozoic.

Today, the Boston Basin is a fault-bound, tectonic lowland filled with volcanogenic sediments and surrounded by resistant highlands of Greater Boston and its harbor. After the final retreat of the continental ice sheet some 14,000 years ago, the landscape directed the Charles River and its tributaries to the sea. As little as 175 years ago, Boston's Back Bay was mired in malodorous mudflats at low tide within an embayment of the river estuary. The time had come for man to re-engineer the natural landscape. If Back Bay was ever to become the urban showcase that it is now and persuade Boston's Yankee elite to remain in town, more habitable land had to be created. But how, with what and from where?

A Glorious Back Bay in Fall From the East
 Immediately east of Back Bay on this side of Arlington Street is the Public Garden, America's first botanical garden. Back Bay is an officially recognized neighborhood of Boston, as are well-known Beacon Hill, the "Italian" North End, Chinatown, Southie and 19 others around town. Many of its neighborhoods were municipalities that were annexed over time as opposed to Back Bay that was "made" by filling in the waters of The Charles. 

For the interest of everyone familiar with the city, I have included present-day landmarks parenthetically. This is the first post of two on Back Bay's geological journey, only in reverse order.
Part I - The Filling In of Boston's Back Bay
Part II - The Geological Evolution of Back Bay's Boston Basin

WHERE IS BACK BAY?
Ask any Bostonian. They'll probably delineate Back Bay by its boundaries with Arlington Street on the east (they might even include the Public Garden), Charlesgate on the west (near Kenmore Square), the Charles River on the north (along Storrow Drive) and the tall buildings of Boylston Street on the south. But, they'd only be partially correct. 

Back Bay is considerably larger - more than twice the area - if you include land created by filling in the shallow embayment of the Charles River on the "back" of the bay, the assumed derivation of its name. That would extend it further south to a narrow isthmus of land that once connected the peninsula on which colonial Boston was located to the mainland. 

Boston Basin - its city, its harbor and its Back Bay
Built completely on filled in land of an embayment of the Charles River, Back Bay's residential district is readily recognizable with its rectangular shape and orderly arrangement of streets and buildings. In the middle distance is Beacon Hill and Flat across Beacon Street from the Public Garden and Boston Common. The tall buildings in the foreground are in Back Bay's commercial district, while those on the skyline include the West End, Government Center and the Financial District on the Shawmut Peninsula of Old Boston. Barely visible is Charlestown across the Charles River from the "Italian" North End.

Back Bay is one of over 20 neighborhoods within the city of Boston. Use this easy to remember jingle to get oriented: Southie is South Boston, but the South End is just that. Directly west of East Boston or Eastie is the North End, which is east of the West End that doesn't exist anymore. The center of Boston is Roxbury, and from there, the South End is due north. North of the South End is East Boston, which lies directly east of the South End, while southwest of East Boston is the North End. As for Back Bay, it's been filled in for over a hundred years. 

Don't look for signage. It's probably not there. Don't try to drive in town. The one-ways always seem to go in the wrong direction. You'll come to know the meaning of the New England phrase, "You can't get there from here." Lost and confused? Stick to the historic Freedom Trail of red bricks embedded in the sidewalk or just use your GPS. Plug the following co-ordinates into any online mapping program such as Goggle Earth and travel to the center of Back Bay: 42°21'04.73"N, 71°04'49.31"W

A TALE OF TWO CITIES - ONE OLD AND ONE NEW
Since its establishment, Boston has increased in size dramatically. It's easiest to grasp the magnitude on a map of the 1630 city superimposed on a map of the modern one. Surrounded almost entirely by water, everything outside the old city's shoreline (dotted line) is land that has been created by filling in between wharves and within dams and seawalls to a level above the high tide. Everything within (light brown) denotes land of the original Shawmut Peninsula including the Neck to the mainland. 

Titles (in red) are many of Boston's annexed towns, neighborhoods and districts. Take special note of the Mill Dam, "Cross Dam", the Full Basin and Receiving Basin, and Beacon and Washington Streets. Their histories are important in the evolution of the city and Back Bay in particular.

Map of Colonial Boston in 1630 Superimposed on a Map of the Modern City
With its orderly grid of streets along the Charles River, Back Bay is readily recognizable in map view. The filling of an embayment of the river extends to the narrow isthmus of land between the peninsular city and the mainland traversed by Washington Street, the only road to the mainland at the time. Boston's neighborhood of the South End now includes a portion of the original landfill.
Modified from Mapworks 2005.

The original area of about 487 acres is currently surrounded by about 500 acres of filled in land, essentially doubling it in size. Note that the colony included Boston Common but not the adjacent Public Garden, which was marshland on the western shore of the peninsula. Compare (above) the random, densely packed, meandering streets of the old city to the orderly, planned grid of Back Bay that was filled in well after the Garden was established.

The modern city of Boston, which has an area of 89.6 square miles, remains 54% land and 46% water, even with its history of extensive landmaking! Boston has always had a unique and intimate relationship with the sea, while Back Bay has had one with the Charles River. Surely, the sea and river have directed the evolution of both, in part, the subject of this post (with lots of history thrown in).

Maps Displaying Boston's Growth Between 1795 and 1912
Whether by annexation or filling in land, the area of Boston has increased exponentially.
Modified from radicalcartography.net

WHAT IS BACK BAY?
It's an officially-recognized neighborhood of Boston, having been reclaimed from shallow estuarine wetlands - tidal mudflats and salt marshes of the "Charles" - beginning some 175 years ago over the course of 100 years. Although many waterfront cities are built on filled in land, likely Boston and certainly Back Bay have more than any city in North America.

Back Bay's residential district is immediately recognizable by its uniformity, lack of high-rises, rectangular shape paralleling the river, orderly grid of gas-lit streets lined by rows of architecturally-significant nineteenth century churches and buildings, and its Paris-inspired, broad Commonwealth Avenue and tree-lined mall running down the center. On Back Bay's south side, the commercial district is the "High-Spine" of buildings, fashionable shops and galleries of Newbury and Boylston Streets. This is the Back Bay that everyone readily acknowledges, but in reality, it extends further to the south away from the Charles River. More on that later.  

A Welcomed Sign of Spring in Back Bay - Dogwoods and Magnolias in Full Bloom
From Andrew Harper

You'll repeatedly hear the same adjectives used to describe Back Bay (especially in real estate ads with prices that are through the roof) - upscale, unique, prestigious, civilized, historic, elegant, serene, fashionable, trendy, chic, sophisticated and affluent. What's interesting about Back Bay is that it isn't one of those parts of a city that acquired those descriptives over time or by urban renewal or radical makeover; it was that way from the start by intent. It was filled in and built up using a carefully planned design that was motivated by political, sociological and geological factors. 

WHAT WAS BACK BAY?
Only 175 years ago, Cambridge and Boston were separated by nearly two miles of river water flowing gently to the sea and thousands of acres of brackish-water wetlands. The Charles River "was" an estuary with a free connection to the open sea and received an in-flux of salt water from the Boston Harbor twice daily. The region that Back Bay now occupies was formerly an embayment of the Charles River. 

Larger than a cove but smaller than a bay and before filling in, it was bordered by foul-smelling (although natural) mudflats punctuated by braided streams and a salt marsh, flooded and drained by saltwater brought in by the tides. Various transgressions of the growing city heightened the people's awareness of the mudflat's odors.

A Typical Estuarine Salt Marsh and Mudflat

Back Bay was constructed in the nineteenth century above the level of the high tide to minimize the risk of flooding. These days, the river is officially the Charles River Basin. Flood-controlled, placid, lake-like and no-longer free-flowing into the sea, the river was impounded at the mouth by the Charles River Dam erected in 1910 and 1979 (although in the course of the river's history numerous mill dams existed upriver). That virtually eliminated the tidal mudflats and tidal flux of the river estuary (not so upriver where it's punctuated by numerous thriving wetlands), although denser cold water still enters the basin through any of three locks in the dam that are opened for navigation.

WHAT'S IN A NAME
Back Bay's parent Boston lies on the Atlantic Coast of eastern Massachusetts where the Charles River meets the sea. It's the 48 square-mile capital of the Commonwealth of Massachusetts, designated as such by the English for the "common good" and a reminder of the colony that England ruled before 1776. 

The city was first called Trimount, alluding to its three dominant hills, all drumlins of glacial origin. They have since been either whittled down or completely eradicated from the landscape to fill in various parts of the city. Boston was renamed by the Massachusetts Bay Colony, whose most prominent members were from Boston, England, a small port in the county of Lincolnshire. It explains the derivation of the town names scattered throughout New England.

Trimount
At the time of settlement, colonial Boston had five hills of varying size, three of which comprised Beacon Hill. Fort and Fox Hill were completely removed for the filling in of land, while the third, the three-peaked Trimount, was gradually reduced to one and is now Beacon Hill. The summits are remembered in the name Tremont Street that courses along the base of Beacon Hill and the name of the original settlement.
From Gleason's Pictorial Drawing-Room Companion periodical of 1850, Courtesy of the Trustees of the Boston Public Library/Rare Books and Wikimedia Commons 

As early as 1858, Boston was referred to as the Hub of the Solar System or simply "The Hub"(referring to the gold-domed State House and coined by poet Oliver Wendell Holmes, Sr.). Other monikers include Beantown (of debated origin), Titletown (goes without saying), Athens of America (a city of educated, spiritual and cultural guiding-members), the Cradle of Liberty (all those revolutionary events), America's Walking City (with its many neighborhoods and Freedom Trail) and the shining "City Upon a Hill" (from Jesus's Sermon on the Mount and delivered aboard the sailing ship Arbella by John Winthrop to his Puritan shipmates on arrival to the New World). The "hill" refers to the glacial landforms of the peninsula (and everywhere in the Northeast) and Winthrop's idealistic vision of the New World. 

The Boston Common, Beacon Hill and its Flat
The gold-domed Massachusetts State House proudly resides near the crest of Beacon Hill on the northeast corner of the Boston Common across from Beacon Street. The Flat of Beacon Hill, along the Charles, rests on landfill. The steepled Park Street Church marks the Common's southeast corner. The Longfellow "Salt and Pepper" Bridge crosses a languid Charles River Basin to Cambridge's Kendall Square neighborhood. History is everywhere, inescapable and connected by the Freedom Trail.

LAY OF THE LAND
The Shawmut Peninsula...
Almost an island, the 789-acre peninsula that the Puritans first settled pendulously jutts into Boston Harbor. It was called Shawmut by Algonguin-speaking Native Americans, possibly of the Massachusetts tribe. The name is thought to be derived from Mashauwomuk, which may allude to the saltwater that surrounds the peninsula or the freshwater springs that enticed the Massachusetts Bay Colony to settle there. It was defensible, well forested, dotted with hills and graced with the necessity of freshwater. Water and geology have always been a factor in the evolution and destiny of the city of Boston.

"Colored Plan of Boston and its Environs"
A pendulous Shawmut peninsula, the location of colonial Boston, juts into Boston Harbor, suspended from the mainland at Roxbury by the Neck, as the Charles River delivers freshwater to the sea. Before damming, the unimpeded river was brackish from the mixing of saltwater and freshwater for miles upstream. Today, nothing remains of the tidal estuary that was once the lower Charles River. It's an entirely man-made waterscape/landscape. To the west of Shawmut is the small, shallow peninsula of Gravelly Point and to the south lies Dorchester Neck. Across the Charles to the north is the colonial settlement of Charlestown.
Modified and cropped inset from 1773 map of Boston by Lt. and artist William Pierie from King George III's collection and the Norman B. Leventhal Map Center at the Boston Public Library

As the population of the new settlement grew within the confines of the peninsula, it developed its famous and infamous, haphazard arrangement of streets that still exists today, some 400 years later. The narrow and crooked "cowpaths" - a myth initiated and now perpetuated in a poem by Oliver Wendell Holmes, Sr. - remain the bane of confused drivers and lost sightseerers in the oldest part of town. 

The confusion is apparent in a photograph taken from a hot-air balloon in 1820. As more space on the peninsula was needed, "wharfing out" was employed, which consisted of filling in the slips (or docks) between wharves as they were extended, which gradually increased the dimensions of the city circumferentially. In time, Bostonians looked to the embayments and coves around the peninsula to create space to grow.

"Boston, As the Eagle and the Wild Goose See It"
Boston's hodgepodge of streets remains to this day, a vestige of the old city. For orientation, the steepled Old South Meeting House is on Washington Street, which slants across the photo. It was the longest street in Boston and the only way to reach the mainland before Beacon Street, which, as we shall see, was related to the filling in of Back Bay. This was the first aerial photograph in America in 1860 by Block and Whipple from a hot-air balloon tethered 1200 feet above the city.
From Smithsonian.org  

The Neck...
When Boston was first settled in 1630, the peninsula was connected to the mainland by a narrow, rather tenuous low-lying isthmus of land called The Neck. It united the colonial city of peninsular Boston to the mainland at the town of Roxbury. Only 50 to 100 feet wide in places, it frequently flooded in storms and was threatened at high tide. As early as 1735, wooden "wharffes", and by 1790, stone wall dams were erected to hold back the sea. 

1776 Map of Boston Showing the British Lines on The Neck
Washington Street was named in honor of George after the American Revolution with every cross street changing its name out of respect. Thus, Winter becomes Summer, Kneeland becomes Stuart, and State becomes Court, the latter being King and Queen before the Revolution.
From the Library of Congress

There was room for only one road across the Neck from Boston to the mainland at Roxbury. It went from from Cornhill Street to Marlborough to Newbury and finally Orange near the mainland. After the American Revolution, in honor of George, its names were unified into Washington Street with street names that cross it changing their names out of respect. It was the Commonwealth's longest street and continues through Roxbury to the Rhode Island state line. It's roughly paralleled by the tracks of the MBTA's Orange Line that inherited its name from Orange Street. 

As for the town of Roxbury, like so many others that surrounded Boston, it was annexed in the nineteenth century, 1868 for Roxbury. The "dissolved municipality" is one of 23 others (including Back Bay that was later "created") that are now official neighborhoods of Boston.

1775 Print of the Neck with British Lines and John Hancock's House
The phrase "One by land, and two if by sea", coined by Longfellow in his epic poem, describes the signal to alert the Patriots about the route the British troops might choose to advance to Concord. Unknowingly, it also describes the routes the two Sons of Liberty chose to leave the Shawmut peninsula of colonial Boston. Paul Revere's 1775 "Midnight Ride" began with a north crossing of the Charles River by water, in this case rowboat, before heading to Concord, while William Dawes galloped into oblivion via a land route across the Neck, just in time before the British sealed off the town of Boston on the Neck. His mission was to warn John Hancock, just off the Neck, and Samuel Adams to avoid their arrest and then join Paul in Concord.
Painting by British officer and surveyor William Richards, Norman B. Leventhal Map Center of the Boston Public Library

"The Charles"...
Boston's famous and infamous river was named by the Prince of Wales, soon to be King Charles I of England. New England's waterforms and surficial landforms are products of the last advance and retreat of the late Wisconsin Laurentide Ice Sheet that flowed through the region between 30 and 15,000 years ago. It left a thick blanket of unconsolidated till, outwash sands and gravels, and glaciomarine clays and silts, some of which formed prominent drumlins and eskers across the landscape that played a role in the creation of Back Bay. 

With a watershed of 308 square miles and flowing through 35 cities and towns, the lazy Charles River makes its way to the sea. Roughly within Route 128 (currently I-95), the ring-road that surrounds Greater Boston, the river enters the Boston Basin and erodes through bedrock of the Cambridge Argillite (much more on that in post Part II) that floors the city and Back Bay (much more on that in post Part II). Before emptying into Boston Harbor, the unimpeded River Charles flowed between Cambridge and Charlestown on the north and the Shawmut peninsula and its Neck on the south. 

Lower Charles River Basin
Facing east, a surface frozen Charles River flows beneath the Longfellow Bridge past the Museum of Science and then swerves to the right ending at the Charles River Dam. The ancestral river was a tidal estuary of Massachusetts Bay - carrying tidal water seven miles upstream as far as Watertown - on the Atlantic Ocean and partially drained at low tide and was brackish at high. These days, in spite of the new Charles River Dam built in the 1970's (the original was built in 1908), the waters are brackish, since denser saltwater flows beneath freshwater when boats enter locks from the Inner Harbor.
Wikimedia Commons

South Cove and Bay...
Immediately north of the Neck and west of the peninsula lay salt marshes and mudflats exposed at low tide sliced by braided networks of stream channels of the river estuary. Originally 737.5 acres in extent, the bay was unequally divided by a small promontory called Gravelly Point (in the vicinity of today's Massachusetts Avenue) that left the largest portion to the east. The embayment eventually succumbed to the the city's growing pains by being filled in as did the cove on the south side. 

On the south side of the peninsula, between The Neck and Dorchester Point/Neck were South Cove and South Bay. After filling in that began in the late eighteenth century, the area became the Leather District, Chinatown and the confusion of "Big Dig" ramps to Fort Point Channel, which is a stunted river-like remnant of South Bay.

FIRST TO MAP
Captain John Smith of the Virginia Company of London explored, mapped and named coastal New England and many of the bodies of water from Penobscot Bay in Maine to Cape Cod, Massachusetts in 1614. The newly-penned River Charles emptying into an island-studded, as yet unnamed Boston Harbor appears on his map. He surely must have seen Boston's many hills from Boston Harbor. 

A young Charles, Prince of Wales, the future King Charles I, provided much of the region's nomenclature, most of which does not survive today. Notable exceptions are the River Charles, Cape Anne and Plymouth. Boston appears on this pre-settlement map, since its the ninth to have been produced. It provided much of the incentive for the English to settle in eastern Massachusetts in the following decades.

The Foundation Map of New England Cartography Dated 1614
John Smith's map, of which there were numerous, was published in 1616 with his A Description of New England. It was a self-promotional propoganda piece for Smith and the Virginia Company advertising the fertile land, abundant resources and general plentitude to found in the New World. It was a place for settlers to start their lives over and was in opposition to the reasons the Pilgrims and Puritans set out for migrating to the New World. The location of the Boston Basin is encircled. The geologic entity was not to be described for over 250 years.

FIRST EUROPEANS TO SETTLE
The dissenting Anglican priest William Blackstone first settled on farmland of the future Boston Common. He invited the group of Puritans that had settled on the peninsula across the river in future Charlestown (another neighborhood of Boston) in 1629 to make the switch in 1630, since the only freshwater spring was accessible at low tide. They were Protestants escaping the sins of Stuart London and seeking a reformed or "purified" form of religious freedom in the New World under the leadership of John Winthrop, lawyer and first governor of the Massachusetts Bay Colony. 

Blackstone eventually departed for Rhode Island, weary of their intolerance of anyone that disagreed with them in spite of their intolerance of the Church of England. On the land that Blackstone had vacated, the Puritans established the city of Boston. 

"Arrival of the Winthrop's Ships in Boston Harbor"
With John Winthrop and his Puritans onboard, the Talbot, the flagship Arbella and the Jewel left England for America on April 8, 1630. The hills of Boston are in the background.
Image courtesy of National Archives by American artist William F. Halsall c. 1880

CUTTING DOWN SHAWMUT'S HILLS
One of the earliest land reclamation projects that Boston undertook occurred in the 1640's, soon after the colony had been settled. It's relevant because of where the earthen material came from, how it affected the landscape and the precedent that it set. It began with a large cove that was dammed off on the peninsula's north side and converted to a reservoir. It supported a number of grist mills for grinding corn and wheat into flour, distilling rum, sawing lumber and even milling chocolate. 

They were tidal mills - powered by the slow release of river water from Mill Pond at low tide that entered from sluices of the West Floodgate at high tide. The concept dates back to Roman times on the River Fleet in London. Once the tide periodicity was predicted, it became a renewable energy source free from drought and with saltwater that didn't freeze in winter. 

Top: Mill Pond and Dam in 1805 With the Mill Pond impounded by the Mill Dam, water from the Charles at high tide entered the West Floodgates and was released at low tide to power the mills. Bottom: Bulfinch's Triangle in 1814 The triangular street plan that was created in the filled in pond became known as the Bulfinch Triangle, the work of the illustrious architect Charles Bulfinch in 1808 and is preserved as a historic district. Modified from Norman B. Leventhal Map Center of the Boston Public Library

But by the end of the 1700's, the mills had become unproductive and left to deteriorate, while the pond had become sediment filled, polluted by wastewater and seepage from residential privies and a "capacious receptacle and reservoir of all the filth and putrescent substances of (the) town....covered with the putrid bodies of dogs, cats, and other animals...offensive and unhealthy." The townspeople rightfully considered it a health risk in the common notion at the time that diseases occur from noxious vapors or miasma. Malaria is a classic example, which means "bad air" in Medieval Italian. 

FILLING IN THE POND
After seven years of debate, the solution was to fill in the pond in spite of losing its "cheering westerly breeze." In 1807, the project began by "cutting down" Boston's hills. The initial contribution came from a portion of Copp's Hill in the North End (a stone retaining wall marks the site alongside the 1659 North Burying Ground). By the early 1820's, much Trimountain's three peaks had succumbed, largely from the middle and highest called Beacon Hill.  

The excavation was accomplished with hand tools and transported via horse-drawn tip-carts to the Mill Pond. The 21 year project added some 50 acres of land to Boston at Mill Pond and was the beginning of Beacon Hill's diminution but not elimination. The story of Boston's missing hills is part of the story of the creation of Back Bay. 

Beacon Hill from the Top of Mount Vernon Street
The drawing of the excavation is in the rear of the present-day State House. The three peaks of Trimountain include Beacon Hill (originally Sentry Hill), Pemberton Hill (Cotton) and Mt. Vernon (or Mt. Whoredom for its red light district). When you visit Boston's State House, note that the monument has been moved from its original location. Bullfinch's column that was perched on the half demolished hill was taken down. The eagle and tablets are preserved within the State House, while a replica the site today. Nearby, William Thurston's house above Bowdoin Street eventually succumbed to the excavation and was torn down, which resulted in a celebrated lawsuit.
Drawing by John Rubens Smith, 1811 and Boston Athenaeum.

For familiar Bostonians, the filled in cove lies between the West and North Ends and the Government Center Garage to the TD Boston Garden and North Station Rail Terminal, which are just outside the dam. Causeway Street was built along the embankment of the Mill Dam, while Canal Street runs along the site of the intended connection with the Charles River. Now a historic district, the Bulfinch Triangle has preserved its original street design for residential, warehouse and commercial use.

1895 Drawing of the Filled in Mill Pond in 1828
Archaeological excavations during the Big Dig project to submerge the highway uncovered remains of wharves, docks, bulkheads, landfill and living spaces from the 17th through 19th centuries. An early success of the filling in of the Mill Pond was the creation of an extension of the Middlesex Canal to Charlestown. Notice the ships travelling from right to left through the canal and the open draw bridge along Causeway Street, which fronts the Boston Garden on the modern landscape.
From Boston Athenaeum and Wikipedia Commons

THE FILLING IN OF BACK BAY
Most Bostonians are aware that Back Bay resides on filled in land, but the perception is that the official process was initiated in the late 1850's. Although it's technically not a part of Back Bay, the project actually began immediately to the east of Back Bay at the site of the future Public Garden. Surprisingly, it was precipitated by a seemingly unrelated catastrophe on the opposite south side of the peninsula. 

In 1794, seven ropewalks and 96 buildings burned down at Fort Hill, one of the region's many glacially-derived hills now long gone (the site of present International Place). Ropewalks were long and narrow, usually wooden buildings where men walked backwards while twisting spun hemp into rope, essential for Boston's fleet of sailing ships to secure anchors and rigging. Dry hemp dust often ignited by open flames of tar vats used to make rope more water-resistant. As a result, ropewalks frequently burned to the ground with everything around them, which is why they were allocated to the outskirts of cities.

Print of an Early Ropewalk
The majority of early coastal communities, irrespective of their size, had ropewalks, a necessity in the days of sailing vessels and the mining industry. Boston had 14 of them in 1794. The illustrator took the liberty of making the rope appear far shorter than it really was. You can visit a preserved ropewalk at the Charlestown Navy Yard across the harbor from Boston. At over 1,300 feet long, it is the only standing facility in existence in the United States, which survived due to its stone construction and is a pending Boston Landmark. 

Following the fires, the ropewalks were relocated to the western side of the peninsula at the foot of the Common (red ellipse). To accommodate the construction of the 700 to 900 foot-long buildings, a seawall was built to facilitate the filling in of the adjacent wetlands. But by 1822 and numerous fires that had struck again, the city, concerned about proximity to the Common, acquired the ropewalk land and adjacent mudflats used for dumping trash and soil. 

1805 Map of Boston Showing Ropewalks at the Foot of the Common
Separated from the Common by Charles Street, the ropewalks were built on made land from wetlands on the west side of the peninsula.

After a lengthy debate as to whether the acquisition should be developed for residential use, annexed to the Common or remain "open and free" to bathe the city in "a constant current of fresh air", the city, in 1825, approved taking earth from nearby Fox Hill to fill in the ropewalk land and grade it down to the river. Unknowingly, land was created for the new Public Garden, which also was the "unofficial" beginning of Back Bay in a manner of speaking.

A PUBLIC GARDEN BEGINS TO FLOWER
Established in 1837 when philanthropist Horace Gray petitioned for the use of the land, it's the first public botanical garden in the United States. The Public Garden is incorrectly regarded as part of Back Bay. It's actually an independent entity separated by almost 200 years of creation by Arlington Street, the first cross street of Back Bay. Its 24 acres are criss-crossed with strolling paths, brightly colored flowerbeds, happy ducks (both alive and statued) and a suspension bridge over a lagoon replete with swan boats. 

With the Boston Common immediately to the east that predates its establishment and the Commonwealth Mall to the west that postdates it, they comprise the northern terminus of Central Park architect Frederick Law Olmsted's "Emerald Necklace." It's an 1,100 acre, seven mile-long chain of eleven connecting parks and waterways throughout Greater Boston that "hangs from the neck" of the Shawmut peninsula. Several components of the Emerald Necklace pre-date the plan to unite them.

The Tranquil Lagoon of the Public Garden
Upon visiting this sublimely serene and idyllic enclave in the middle of the city, it's hard to believe not only that it's in the center of town but that it was once submerged beneath a shallow, muddy edge of the Charles. It's reminiscent of beautiful Parc des Buttes-Chaumont of Napolean III in Paris that emerged from a bleak gypsum quarry and refuse dump for sewage and horse carcasses. You can read about it here.

Proof of submersion are 4, to 5,000 year-old staked remains of fish weirs discovered during construction of the Boston Common Parking Garage across from the Garden. Native Americans used the ebb and flow of tides in the Charles estuary to entrap fish as brackish water flowed back to the sea, just as the mill dams harnessed the tides to power textile mills. They would be used once more in Back Bay before its filling in.

Artist Depiction of Boston Fish Weir Some 5,000 Years Ago
The stakes of fish weirs were first discovered in nearby Boylston Street in 1903, during the excavation of the subway line and later during the construction of high-rises in Back Bay.
From fishweir.org

THE SECOND MILL DAM OR THE INDUSTRIALIZATION OF BACK BAY
Reminiscent of the Mill Pond, Back Bay's filling began as a power project, when, between 1818 and 1821, an ambitious dam was built by the Boston and Roxbury Mill Corporation. The one and a half mile-long Great Dam extended across Great Bay - the embayment of the Charles River - from the foot of the Common (intersection of Charles and Beacon Streets) on the east to Sewall Point in Brookline (Kenmore Square) on the west. It was intersected by a shorter cross-dam that ran from the low peninsula of Gravelly Point (today's intersection of "Mass" and "Comm" Avenues). 

The two dams divided Great Bay in two. Upriver on the west was Full Basin that received water at high tide through five pairs of floodgates. Water was then shunted through sluices to power mills located on Gravelly Point and then through raceways at low tide to a larger Receiving Basin downriver (the part that is known as Back Bay), and finally back out to the main river. The intent was to power the mills to serve and give Boston a competitive edge over steam-powered mills in New York and Philadelphia, while costing less than obtaining items from Europe in short supply from the War of 1812. 

The 50 and later 200 foot-wide Great Dam housed Western Avenue, which was the forerunner of today's Beacon Street (much of the dam is buried beneath it). Originally, Beacon Street only ran a short distance down Beacon Hill next to the Common as far as the waters of Back Bay but later linked colonial Boston with Brookline to the west as did Washington Street with Roxbury 200 years before. In the mid-1840's, the BRM Corporation added a short seawall at the Boston end of the dam that increased the width of the Mill Dam. Eight adjoining houses soon followed. Back Bay was starting to populate!

Map of Boston and Environs Before the Back Bay Reclamation Project c. 1855
The once narrow Neck has been widened for the development of the South End in the region of Washington Street and south. The solid ellipse encompasses an unfilled in Back Bay, criss-crossed by the Mill Dam, cross dam at Gravelly Point, two railroads travelling on raised embankments through the center of the Great Bay and a ghosted street and lake design for Back Bay. The tracks of the Boston and Providence and Boston and Worcester railroads cross within the Receiving Basin. The Boston Common and adjacent Public Garden (green) await the initiation of landfill for Back Bay. The Charles is still a free-flowing river, crossed by a network of rail lines that converge flats of the filled in Mill Pond on the peninsula's north side (dotted ellipse).
Modified from Joseph Hutchins Colton map from Colton's Atlas of the World, 1856

ARRIVAL OF THE IRONHORSE
In the 1820's, railroads began to appear in Boston. Inspired by the advent of steam-powered railroads in England and the horse-drawn railroad locally that brought blocks of granite down from the Quincy Quarry for construction of the Bunker Hill Monument in Charlestown, they came from Lowell, Worcester, Providence, Maine and New York. By the end of the nineteenth century, eight separate railway terminals existed in Boston, which were consolidated to two. Rail lines criss-crossed the Charles on elevated embankments as they heading to the flats north of Causeway Street (the site of the Mill Pond at today's North Station), from the south (at South Station, which coincided with final landmaking in the South Cove in the 1890's) and the future Back Bay. 

Trains Crossing Back Bay in 1844
Viewed from the Cambridge side of the river (near the Mass Ave MBTA Orange Line Station), much of the Receiving Basin can be seen. A passenger train of the Boston and Providence Railroad (now Amtrak), riding on an elevated embankment, heads in the direction of the State house and will cross (near the Back Bay Orange Line Station) the rails of the Boston and Worcester Railroad (the commuter rail along the Mass Pike), seen at the far left. Little regard or comprehension of the adverse ill effect of preventing natural river flow existed at the time.
From bostonbackbay.com

The railroads were highly welcomed in the commercial competition that was developing with New York, Philadelphia and Baltimore. They not only became the principal reason for creating land in the second and first halves of the nineteenth and twentieth centuries (largely at the expense of Mount Pemberton, Trimountain's easternmost peak), but the railroads were the means by which Back Bay was filled in. Without them, the task would have been far more laborious and lengthy.

HISTORY REPEATS ITSELF, YET AGAIN
In the mid-1840's, it was clear that tidal power and the capacity of the Receiving Basin were insufficient. The Corporation had envisioned some 81 mills and a major industrial district, but only four were operational at one time. Worse, damming impeded the river's natural flow and beneficial tidal flushing twice daily as did the network of railroad embankments that "roofed the river" in addition to interfering with navigation. The entire situation was worsened by the spillage of raw sewage and the dumping of waste. 

Back Bay had become a "great cesspool (with)...a greenish scum"...whilst the surface of the water (was) bubbling like a cauldron with the noxious gases...exploding from the corrupting mass below." With an 1849 cholera epidemic in the overcrowded and unsanitary Fort Hill district fresh in the minds of the townspeople, the perceived health hazard was real.

Map of Sewers Draining Directly into the Back Bay's Southeastern Shoreline in 1850
 The Receiving Basin was kept as close to empty as possible in order to maximize infilling at high tide. As a result raw sewage from 18 sewers from the east and south shorelines of the Neck land discharged onto the mudflats and accumulated at the shoreline, additionally cut off from from river flushing by the Mill Dam and railroad embankments.
From Newman and Holton and the State Library of Massachusetts

With metropolitan Boston's population increasing (571,789 in 1850), the more profitable and productive use of the tidal mudflats was to convert it to habitable residential land. The small and confining Shawmut peninsula of old Boston had fulfilled its requirements of a defensive position, a high point for the location of a beacon to warn ships at sea, and freshwater springs and wells. But in 1850, overcrowding occurred as the population quadrupled in 40 to 50 years. 

Two solutions to the problem became obvious - either improve the bay's drainage or fill it in and convert the "putrid worthless marsh" to "solid and wholesome dry land" with "clean gravel" rather than with perceived unclean, clay-rich (poorly-drained) dredged river mud. The latter option was agreed upon, but, there was another reason - a covert one that was both political and sociological in motivation and related to Irish potatoes. 

GROWING PAINS AND EMIGRATING IRISH
Starting in 1845, a virulent fungal blight devastated the potato crops in Ireland. It deprived Irish families of their main source of food and subsistence and was responsible for over a million lives lost from famine and another million that emigrated to America (read about it here). 

In 1847 alone, 37,000 Irish refugees landed in Boston on the edge of death and despair, which almost instantly made the Irish a quarter of the city's population. The development of the South End, in addition to providing more living space, was an attempt to encourage members of the upper middle-class to remain in town as tax payers and voters to counter the arriving masses of impoverished and struggling Irish Catholics - unskilled, unemployed and unwise to the ways of city life. But things changed in the 1860's when the desirability of many neighborhoods including the South End diminished for the city's Proper Bostonians, who would became increasingly attracted to the grandeur of Back Bay.

Irish Famine Memorial on the Freedom Trail at the Corner of Washington and School Streets
The roughest welcome to the emigrating Irish was in Boston. With no one to help them, they settled into the lowest rung of society and began a daily battle for survival. “Native Bostonians might have been willing to send money and food to aid the starving Irish, as long as they remained in Ireland,” wrote historian Thomas H. O'Connor. Despite hostility from some Bostonians and posted signs of "No Irish Need Apply", the Irish transformed themselves from impoverished refugees to hard-working, successful Americans.
Statute by artist Robert Shure

FILLING IN THE BACK OF THE BAY
Filling in the tidal mudflats of the Charles was a concerted but not always seamless and cooperative agreement between the city (such as the Boston Water Power Company), the state and various commissions, flat owners, entrepreneurs and corporations (such as the Boston and Roxbury Mill Corporation) that had a vested interest in its establishment. What was needed was agreement of the interested parties, a design for Back Bay, financing, a plan for filling it in, a source of earthen material and a means of getting it there. 

In the beginning, the majority of sand and gravel came from the town of Needham to the west of Boston. The source were kame terraces and eskers - fluvioglacial depositional structures deposited during stagnation or retreat of the Laurentide continental ice sheet. "Steam-powered excavators" loaded two shovel-fills per car (a six-ton load) onto a gravel train of some 35 cars in length - a 35 minute-job! Needham's loss was Back Bay's gain as fifty foot-high hills were "transformed to a desert." They worked day and night as 145 gravel cars and 80 men made 25 trips per day - loading, transporting and dumping onto the shores of Great Bay's Receiving Basin.

Engraving of Steam-powered Excavator Loading a Gravel Train in 1858
A multi-car gravel train is being loaded. "Back Bay" is written on the tender behind the locomotive. The presence of dignitaries and ladies implies it was either perhaps a planned visit or the artist took creative liberties. Today, the region is largely residential and office parks. It's noteworthy that a beautiful esker is preserved at Cutler Park on the upper Charles River.
From Ballou's Pictorial Drawing Room Companion, Boston Public Library

The railroads that entered Boston in the 1830's provided an inexpensive long-distant means of transporting massive amounts of sand and gravel to the Receiving Basin, although additional spurs had to be added and locomotives, side-dumping gravel cars and steam shovels had to be financed and purchased. The trains made the nine-mile, 45-minute trip to Back Bay by initially taking a spur to the New York and Boston mainline (Penn Central tracks), then to the Green Line's Riverside Branch in Newton, and finally the lines of the Boston and Worcester Railroad (the commuter rail along the Mass Pike) from Brookline to Boston.

A Steam-powered Locomotive and Gravel Train Makes its Way Through the Town of Newton
Jackson Homestead Archival Photograph Collection

Filling Back Bay began in 1858 at the edge of the Public Garden. The defunct Mill Dam provided the retaining structure for the fill. Railroad spurs were continually revised to facilitate dumping further and further outward over the mudflats in the directive of the Mill Dam. Four separate areas of Back Bay were simultaneously filled to speed up the process, while progressing from east to west toward the cross dam. 

Dumping specifications required that sand and gravel be built up over the mudflats so that the elevation of streets were 18 feet above mean low tide called the Boston City Base, which was the level of the Mill Dam, while house lots were filled six feet lower to conserve the transportation of material where basements would be located. Although particular attention was given to concerns over the water table, problems exist across Back Bay's modern landscape related to fluctuating groundwater levels and flooding. Leaks in train and subway tunnels, highway underpasses, basements, sewers and drains lower the water table forcing cracks to occur in foundations and exposing wood pilings to rot and subsequent collapse. 

West and Southwest View of Back Bay c. 1858
In panoramic view taken from the dome of the Massachusetts State House over the rooftops of Beacon Hill buildings, Back Bay was in the earliest stages of filling in. A widened Mill Dam with Western Street running due west to Brookline appears on the right with a newly-built seawall containing new brick housing. Boston and Worcester and Boston and Providence Railroad lines cross the center on mudflats of the Receiving basin on elevated embankments. Notice also the open spaces and strolling promenades of the Boston Common and a newly-planted, tree-lined Arlington Street. The hills in the distance frame the Boston Basin. 
Modified from the Boston Athenaeum 

West and Southwest View c.2017
Here's the approximate view seen above with the gold dome of the State House in the foreground. In all its splendor, the Back Bay (ellipse) has been filled in and built up with the residential district on the north (left) and commercial district on the south (right). Beacon Street heads down from Beacon Hill and then continues on the site of the Mill Dam to Brookline and ends at Newton's western town line.
Image generated on Google Earth

Here's a view of the same landscape in 1855 from the opposite direction, facing east. Again, notice the new construction along the seawall of the widened Mill Dam. Boston and Roxbury Mill Corporation stockholders bought lots and constructed eight adjoining houses, of which two remain. Unfilled mudflats of the Receiving Basin are visible along Arlington Street with newly-planed trees, while mature plantings completely surrounds the Common across Charles Street. Dust blowing east from the flats to the many residential structures that followed were a source of great annoyance to the occupants.

Birds-eye View of Boston Facing East c.1855
This is the exact opposite perspective of the above image. In the foreground are unfilled mudflats of the Receiving Basin. A domed State House resides on Beacon Street that ends on Charles Street and continues out onto the Mill Dam as Western Avenue. Notice the many railroad bridges that converge on the north side of the Shawmut peninsula, all on land fill of the Mill Pond. In the distance, wharfing has significantly expanded the dimensions of colonial Boston into a very busy Boston Harbor sprinkled with Harbor Islands. Everything in view, including the harbor and islands, is within the Boston Basin tectonic depression.
Modified from Boston Athenaeum's digital collection online

Horse-drawn graders then contoured the landscape for streets under construction. Wood pilings were driven through the cover of land fill and underlying mud to hard, marine clay, which was typically 30 to 40 feet below ground surface. As long as they remained submerged in groundwater, they would last for centuries. If groundwater dropped, the pilings would become exposed to air, attacked by microbes, eventually rot and collapse causing severe foundation problems. The potential problem isn't solely Back Bay's but wherever land was "made" in Boston - the Fenway, South End, Bay Village, Beacon Hill Flat, Chinatown, Leather District, Bulfinch Triangle, North End, Downtown waterfronts, Fort Point Channel section of South Boston and parts of East Boston. Observation wells at various locations monitor water levels. (Read about it here).

Buildings were erected starting from Arlington Street at the Public Garden as filling was progressing to the west. The process progressed westward when Massachusetts Avenue was reached in 1870. In time, sand and gravel was obtained from other sources such as Hyde Park, Canton and Dedham to the southwest of Boston. In 1865, the sluiceways of the mills were filled in, a major milestone in the filling of Back Bay. Ultimately, the area to the west that included the Muddy River, a tributary of the Charles, resulted in the creation of the freshwater Back Bay Fens - another link in Olmsted's Emerald Necklace.

ESE Bird's-eye View of Back Bay c.1870
With Commonwealth Avenue's freshly-planted, tree-lined mall leading to the Public Garden across Arlington Street, the buildings are completed and occupied in easternmost Back Bay as far west as Clarendon Street. Beyond, the street grid has been laid out and construction is progressing in various phases with wooden ground piles being driven in to serve as foundations. On the site of the widened Mill Dam are Back Bay's first eight houses (two still stand) on Western Avenue, soon to become Beacon Street. Off to the left (out of view) is the Flat of Beacon Hill.
Modified from artist F. Fuchs and Boston Public Library

BACK BAY TAKES SHAPE
The meticulous planning of Back Bay was realized when construction for residential buildings was initiated as "well to do" families began to move in, even as landfill was progressing just to the west. A conscious effort was made to insure upper middle-class residential occupancy by prohibiting the presence of mechanical, mercantile or manufacturing. Height restrictions, setbacks, facades, number of stories and service alleys at the rear of residential buildings were mandated as well. Even lot sales to the "right sort" were carefully controlled. 

It was apparent that Back Bay would become the antithesis of colonial Boston - "new", flat, clean, orderly, systematic, spacious and well-planned - the result of a multitude of land reclamation projects that were conducted governmentally, corporately and individually. Even east-to-west streets were assigned alphabetical names that alternated di- and tri-syllabically. Beginning with Arlington Street along the western edge of the Public Garden, it's followed by Berkeley, Clarendon, Dartmouth and so on. At Back Bay's western boundary at Charlesgate, where the tributary of Muddy River enters the Charles, the naming convention continues with Ipswich, Jersey and Kilmarnock Streets.

East View of Back Bay from Commonwealth Avenue c. 1885
From the corner of "Comm Ave" and Exeter Street, horse-drawn carriages carry patrons through a most elegant  "new" Back Bay. The mansard-roofed, Second Empire design of the c. 1871 Paris-inspired Vendome Hotel (first in Boston with electric lighting) gleams in Italian white marble compared to the drab "brownstone" of the neighboring Victorian structures. 1,156 buildings were constructed in the residential district. By 2015, 99 had been demolished and replaced with newer buildings, parking lots or playgrounds. The last family dwelling was built in 1908. Visit Back Bay Houses here for a house-by-house, detailed history.
From Boston Athenaeum.org

The architectural design that was employed was systematic as well, although not plan-specified. As filling in proceeded from east to west, construction progressed accordingly and reflected the popular architectural design and building stone - mansard-roofed French Academic, Gothic, Ruskinian Gothic (High Victorian Gothic), Queen Anne and Panel Brick, along with many revival styles such as Italian Renaissance, German Renaissance, Beaux Arts, Chateauesque, Georgian, Federal and Adamesque. 

Boston's proximity to several sources of stone encouraged its incorporation into the construction of Back Bay's buildings. Thirty-six early churches had foundations of Late Proterozoic Roxbury Conglomerate ("puddingstone"). Facings progressively included Portland and Longmeadow Jurassic sandstones ("Brownstones") from the Connecticut Valley and Newark Basin in New Jersey. Common brick was fired from Holocene Boston Blue Clay. Paleozoic granites came from Dedham, Quincy, Chelmsford, Westerly Rhode Island, and the Maine coast, and later Indiana Limestone and Vermont marble arrived by rail. 

LOOKING BACK OVER 400 YEARS OF URBAN EVOLUTION
Back Bay had become the elegant and fashionable neighborhood that had been envisioned. But its evolutionary journey was far from complete once the embayment was filled in and the neighborhood became occupied. In the early twentieth century, the last filling in (east of Massachusetts Avenue) includes the narrow park of the Boston Embankment along the Charles River, later widened to form the Esplanade in the 1930's and the addition of the Storrow Drive highway along the river in 1950.

Here's a look back at Greater Boston in 1873. Present day Boston bears little resemblance to the peninsula that jutted out into the harbor some 400 years earlier.

The City of Boston in 1873 (Click for a Larger View)
Looking west from high above Boston Harbor, the view includes many important additions to Boston's landscape from the 1630 settlement. Back Bay (K) can be seen on Boston's west side with a considerably large, soon to be filled in Muddy River tributary entering the Charles. Across the Charles, the Bunker Hill Monument has been erected in Charlestown (F) and the Naval Yard (G) is in operation with the Mystic River (T) to the north. Cambridge (S) is upriver to the west. Fort Point Channel (L) leads to South Cove Bay (N), yet to be filled in South Boston (M) and Dorchester (P). A domed State House (A) is on Beacon Street that runs alongside the Common (I), Public Garden (J) and Back Bay (K) straight to Brookline (R) and Newton beyond. Old South on Washington Street (D) leads across the filled in Neck to Roxbury (Q) past the South End (O). In colonial Boston on the Shawmut peninsula, note the Old State House (E), Custom House (C), Faneuil Hall and Quincy Market (D) and the many wharves of the Central Waterfront (F). A plethora of rail lines on raised embankments criss-crosses the Charles converging on the Bulfinch Triangle (E), site of the filled in Mill Pond. Everything in view including Boston Harbor (U) and the surrounding uplands are within the Boston Basin.
Modified from a Currier and Ives print, Boston Athenaeum

Tucked into the northwest corner of the Public Garden at the corner of Arlington and Beacon Streets is a dramatic and powerful bronze statue by Daniel Chester French completed and dedicated in 1924. It's entitled "Casting Bread Upon the Waters" from Ecclesiastes 11:1. Entirely meant for a different message, the angel is ironically casting bread upon what was once the tidal waters of the Mill Dam's Receiving Basin.

"Cast They Bread Upon The Waters For Thou Shalt Find It After Many Days"

We've seen what an industrious, dedicated and imaginative group of Bostonians have created in Back Bay by re-engineering the shallow embayment of the Charles River. The only thing left to explain is how Greater Boston and its harbor arrived on the landscape in the first place. Please join me for a discussion in Part II of Urban Geology - The Geological Evolution of Back Bay's Boston Basin. 

MAPS OF BOSTON ONLINE
•  Boston Athenaeum (here).
•  David Rumsey Map Collection (here).
•  Digital Commons at Salem State University (here).
•  Norman B. Leventhal Map Center at the Boston Public Library (here).

SELECTED REFERENCES
•  Avalonian Perspectives on Neoproterozoic Paleogeography: Evidence from Sm-Nd Isotope Geochemistry and Detrital Zircon Geochronology in SE New England, USA by M.D. Thompson et al, GSA Bulletin, 2011.
•  Boston - A Topographical History by Walter Muir Whitehill and Lawrence W. Kennedy, The Belknapp Press of Harvard University Press, 2000.
•  Boston's Back Bay - the Story of America's Greatest Nineteenth-Century Landfill Project by William A. Newman and Wilfred E. Holton, Northeastern University Press, Boston, 2006.
•  Cobblestones, Puddingstone and More: Boston's Use of Stone as an Essential Urban Element - A Walking Tour by Dorothy Richter and Gene Simmons, Guidebook for Geological Field Trips in New England, 2001 Annual Meeting of the GSA, Boston, Massachusetts.
•  Digging up Boston: The Big Dig Builds on Centuries of Geological Engineering by Bradford A. Miller, Geotimes, American Geosciences Institute, October 2002.
•  Gaining Ground - A History of Landmaking in Boston by Nancy S. Seasholes, The MIT Press, 2003. Encyclopedic in content with great maps and images!
•  Houses of Boston's Back Bay: An Architectural History, 1840-1917 by Bainbridge Bunting, 1967.
•  Reinventing Boston: 1630-2003 by Edward L. Glaeser, Journal of Economic Geography 5, 2005.
•  Sedimentology of the Squantum 'Tillite',  Boston Basin, USA: Modern Analogues and Implications for the Paleoclimate During the Gaskiers Glaciation (c. 580 Ma) by Shannon Leigh Carto, Thesis, Graduate Department of Geology, University of Toronto, 2011.
•  The Application of Geographic Information Technology and Ground-Penetrating Radar in the Study of the Evolution of the Charles River Basin by Lars E. Anderas, Masters of Science Thesis, University of Massachusetts Boston, 2013.
•  The Geology and Early History of the Boston Area of Massachusetts, A Bicentennial Approach by Clifford A. Kaye, U.S. Department of the Interior, Geological Survey Bulletin 1476.
•  Urban Geology of Back Bay and Beacon Hill, Boston, Massachusetts by James W. Skehan et al, Guidebook for Geological Field Trips in New England, 2001 Annual Meeting of the GSA, Boston, Massachusetts.