New York City was one of the earliest European settlements in North America and has long been the largest city in the United States. By 1920 the total population of the metropolitan area of New York City had surpassed 7 million people. It was in the 1920's that new technology became available that allowed the construction of buildings over 50 stories tall.

These new buildings were constructed differently than those that typically preceded the building boom of the 1920's and 30's. Skyscrapers of this new era were constructed like the cathedrals of old Europe, with the interior columns carrying all of the load, and the walls only acting as curtains.

The construction of sky scrapers in New York City began in downtown, around Wall St. at the lower end of Manhattan Island, but soon spread north. Here's where things begin to get a little more interesting. New skyscrapers were not being built close to downtown, but rather were mostly being constructed in midtown, 4 miles north.

This has to do in part with the depth of the bedrock underneath the city. Large buildings need to be anchored to bedrock in order to prevent potentially uneven settling. The bedrock is within a few feet of the ground surface in Midtown, and within 40 feet of the surface in Downtown. It is 4 to 5 times deeper in other parts of the city. Skyscraper developers generally shied away from building between these two main business districts in part because the deep bedrock would significantly increase building costs.

Depths to bedrock for Manhattan, south of Central Park
Source: Bedrock Depth and the Formation of the Manhattan Skyline, 1890-1915

Other factors certainly did play a role in the growth of New York City. The locations of residential neighborhoods and manufacturing centers had an influence on the city's development pattern, as well as transportation hubs such as Grand Central Station in midtown. However construction costs due to bedrock depths seems to have a significant influence on how developers chose locations for new skyscrapers. Bedrock depth is one of the many ways that geology can affect the development of cities. In this case creating two separate development zones in New York City.

Below are a few pictures of the city's skyline. You can see for yourself where the bedrock valley lies along the island of Manhattan.

NYC skyline looking North as seen from lower Manhattan
photo credit: New York City (America the Beautiful) by Dan Liebman

NYC skyline looking South