Structural Implications of Walloomsac and Hartland Rocks Displayed by Borings in Southern Manhattan

Over the past three years we have been examining drill core that has penetrated bedrock from various construction sites throughout NYC. Careful examination of rock core, sampling, and petrography have been fruitful in extending mapping to southern Manhattan from areas of natural exposures north of 59 Street. The outcrop and drill core data support the view that at least three distinctly different and mappable schistose units constitute the formation known as the Manhattan Schist. Separated by ductile faults known as the St. Nicholas thrust and Cameron’s Line the schistose rocks, from their structural base upwards, are known as the autochthonous Walloomsac formation and allochthonous Manhattan and Hartland formations.