Jan 05 2011

In the Beginning

Published by at 6:04 pm
Under Topography and Cartography

T

he New York City borough of Brooklyn lies at the western end of Long Island and has a fascinating topographic history that has influenced the course of major historical events on more than one occasion. As with all of Long Island Brooklyn is under-laid with sedimentary layers of rock that strike northeast and are inclined gently to the southeast. These layers appear at or near the surface in the vicinity of Long Island Sound, where erosion has left relatively tough sands and clays at elevations of more than 60 feet above sea level. Further south and resting on top of these sands and clays and forming the highest elevations is a belt of glacially deposited debris composed of an unsorted, unstratified mixture of boulders, sand, silt, and clay. This debris was deposited in the interval between 75,000 and 17,000 years ago when the area was covered by a massive sheet of glacial ice (1) known as the Wisconsin Ice Sheet. This was the last of many glacial advances that grew after the start of the Pleistocene Era about 1.5 million years ago and that stretched down from eastern Canada (Labrador), advancing as far south as New York City.

The Wisconsin Ice Sheet left its marks on the city, depositing rock and debris and accounting for the hilly areas that run straight through the middle of the five boroughs. Geologists believe that the Wisconsin Ice Sheet began its southward journey from Labrador about 90,000 years ago and reached its maximum about 70,000 years ago, forming the Ronkonkoma Moraine on Long Island. Following a period of warmth and retreat, it advanced again starting about 45,000 years ago, reaching New York City about 20,500 years ago, forming the Harbor Hill Moraine and then beginning its final retreat about 18,000 years ago. In North America, the Outer Lands is a name given to the terminal moraine archipelago of the northeast United States (Cape Cod, Martha’s Vineyard, Nantucket, Block Island and Long Island).

It has been said that the Ice Age ended in Brooklyn.

In New York City, the Wisconsin Ice Sheet was 1,000 feet thick (in the Adirondacks it was over 5,000 feet thick and perhaps as much as 10,000 feet thick in Labrador). The Wisconsin Ice Sheet had an impact not only on New York City but also farther north, deepening the bed of the Hudson River Valley (the Hudson River is the southernmost glacial fjord in the Northern Hemisphere), carving out the Great Lakes and the Finger Lakes basins, and leaving its mark on the Adirondack mountains. The glacier also deepened valleys beneath Webster Avenue in the Bronx, and the Harlem and East Rivers. It smoothed the bedrock and left glacial grooves and striations as the advancing glacier dragged rocks over the surface. These can be seen throughout Manhattan’s Central Park. Because the glacier acts very much like a conveyor belt, the longer it stays in one place, the greater the amount of material that will be deposited. The moraine is left as the marking point of the terminal extent of the ice.

The Brooklyn terminal moraine with secondary elevations : 2. Bay Ridge- Dyker Heights 2. Sunset Heights 3. Owl's Head 4. Fort Greene Park 5. Brooklyn Heights

The nature of glaciers is that as they grind away at rock underneath them, rock gets picked up and travels along with the glacier. After the glacier melts, the rock debris is left behind. In the New York region, the Wisconsin Ice Sheet deposited tons of gravel, pebbles and sand—moving, for example, boulders from the Palisades to Central Park—plowed up topsoil, and leveled the earth, filling in depressed areas with glacial till. Even after the Wisconsin Ice Sheet stopped advancing south and its southern end was melting at the same rate that the ice advanced, rock debris continued to be deposited and piled up at the southern edge of the ice sheet. This feature is known as a “terminal moraine” and evidence of it (hundreds of feet high in some places) stretches from the southern end of Staten Island across the Narrows and through Brooklyn and Queens. (2)

The ridge extends in an east northeast direction from the Park Slope section of Brooklyn, with hills of varying heights of 100 to 150 feet, with the southern slope of the ridge having a relatively steep drop and the rear, a more gradual slope. Without the terminal moraine, most of Long Island, including Queens and Brooklyn, would lie beneath the Atlantic Ocean, since the bedrock of Long Island is largely below sea level. In addition, the huge amounts of sand, silt, and clay that form the five-mile wide outwash plain that lies under Flatbush, Coney Island, and Canarsie were deposited by streams from the melting glacier.

The moraine as greenbelt: 1: Green-Wood Cemetary 2: Prospect Park 3: Evergreen Cemetary

Many parks and cemeteries are located where the land was too steep for easy farming or subsequent urbanization. The rocky terminal moraine areas meant that they were the least suited for real estate development, and thus the cheapest lands for the city to use for wood lots, cemeteries, and especially for parks. The band of green across Brooklyn and Queens, from Highland Park to Forest Park, including the many cemeteries in this area, is all built on the terminal moraine. In Brooklyn, Green-Wood Cemetery and Prospect Park both comprise a portion of the terminal moraine, and the moraine is even referred to in the names of neighborhoods across this strip: Bay Ridge, Greenwood Heights, Windsor Terrace, Prospect Heights, Crown Heights, Highland Park, Cypress Hills, Ridgewood, and Forest Hills. It is interesting to note that with the exception of the Bronx, the high points of each borough are in parks or cemetaries: Bennett Park in Manhattan, Todt Hill in Staten Island, Green-Wood cemetary in Brooklyn and Evergreen cemetery in Queens. Many of these ridges and peaks provide stunning views of the Manhattan, and park designs such as Sunset Park and Owl’s Head Park have taken advantage of these vistas in intricate networks of pedestrian paths and terraces.

The Battle Pass area, also known as Flatbush Pass in the area of Prospect Park and Green-Wood Cemetery. An etching circa 1792

In colonial times, the moraine was known as the Heights of Guan. With the advance of urbanization much to the moraine has been leveled off, but to early settlers of the area, these elevations would have appeared almost mountainous. Most of the early roads, which followed the paths of the Leni Lenapi Amerindians, bisected the moraine. During the American Revolution the hills posed an obstacle to the attacking British from the south due to the steepness of the southern slope and the fact that they were densely wooded. There were only four passes through the Heights of Guan: Gowanus Pass, Flatbush Pass (later known as Battle Pass), Bedford Pass and Jamaica Pass. Battle Pass (now in Prospect Park) and Jamaica Pass would figure significantly in the Battle of Brooklyn, the topic of several upcoming blogs.

In addition to the central moraine, the lowland coastal areas of Brooklyn were typically swampland. What is now the Gowanus Canal was originally a tidal inlet of navigable creeks in original saltwater marshland and meadows teeming with fish and other wildlife. Henry Hudson and Giovanni da Verrazzano both navigated the inlet in their explorations of New York Harbor. There were considerable swamplands to the north and east, including the present-day neighborhoods of Red Hook, Williamsburg and Greenpoint.


  1. http://academic.brooklyn.cuny.edu/geology/leveson/linksa/nygeomorph.html
  2. http://www.nycgovparks.org/sub_about/parks_history/geology.html
  3. Gotham: A History of New York City to 1898 by Edwin G. Burrows and Mike Wallace (2000)

2 responses so far

2 Responses to “In the Beginning”

  1. sante says:

    I think of those type O Caribs eating Verrazano…

    My parents grew up in Brooklyn. I never lived there, but I was born there, because my mother’s OB was there, so she commuted. I’m a history buff, Peter, and really appreciate your treatment of Brooklyn here. Keep sending it. It’s a gift to be fascinated by the region one has actually inhabited. I look back at my New York roots and the New England where I went to school and regret that I was so oblivious while I was there. I try to goad the kids into historic interest in their locales, to no avail. I guess most of us don’t catch that bug until midlife or so…

    Thanks.

  2. Kev says:

    It’s good to be educated. Thanks for the info.

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