The reason so many skyscrapers are clustered Downtown and in Midtown isn't so much because of geological feasibility as because everybody else was doing it. It was long assumed that the depth of our venerable Manhattan Schist bedrock, well-suited for the construction of tall buildings, was the determinant in where the city's towers rose. Though the bedrock outcroppings are indeed at their deepest and closest to the surface in the areas where many of the city's tallest buildings are clustered, it's more likely to be coincidence than cause and effect. The real reason there's a big doughnut hole in the spiky man-made terrain between FiDi and Midtown has more to do with the way the city's dual business districts developed from a sociological and economic perspective between 1890 and 1915.
Find out why the bedrock myth is on shaky ground