Note.—The Ice Age has been divided by some geologists (Chamberlin, Saulsbury, Leverett) into two epochs—an early and later Ice Age—between which a reforestation of areas, made bare and desolate by the ice, took place; by other geologists (Wright, Fairchilds) the Ice Age is regarded as a continuous period, with retreat and advance of the ice cap over long intervals.
GEOLOGICAL POSITION OF THE ROCKS OF NEW
(GREATER NEW YORK)
As determined by the State geologists, the rocks of Manhattan Island represent the Archaean, Cambrian, Calciferous-Trenton (Ordovician), Hudson River, with injected igneous masses, dikes, etc., and a superficial covering of drift, river muds, and sands. This assumption is controverted in the text.
(BOROUGH OF KINGS AND QUEENS)'
foundation Archaean on this overlying schists (Hudson River) ;
possible underlying Cretaceous beds, not exposed within city limits;
superficial drift, shore sands.
BOROUGH OF THE BRONX
Archaean, Hudson River, Calciferous-Trënton (Ordovician) igneous intrusions, drift.
(BOROUGH OF RICHMOND)
Central hills made up of Serpentine (eruptive and meta-morphic), basal crystalline rocks similar to Manhattan (now