Jerome
Avenue, a section of limestone " plainly rolls over the schist, while a
little way below, on and near Jerome Avenue, a considerable series of
limestone layers dip eastward, showing overlap." Mr. Yeshilian
considers the contour of contact between the limestones and the schists
a fault line at Inwood (Dyckman Street), towards the Hudson, at Fort
George, and along the Harlem River defile at High Bridge and
Washington Bridge. In the limestone at Girard Avenue and 167th Street,
according to this observer, there are very noticeable enclosures of
gneiss or schist in the limestone.
Mr.
E. C. Eckel has published his observations of a locality at the
northern end of the island, a few blocks north of Fort George, at
Hawthorne Street, between Maple and Sherman Avenues, where the
limestone is cut by a pegmatite or granite dike, giving rise near the
contact to tremolite, biotite, and tourmaline. On Post Avenue, just
north of 204th Street, the dolomite (limestone) flooring the lowlands
appears in platy beds, in thin sheets, lamellarly curvilinear, and
forms a bank (12 feet high) along Post Avenue (Fig. 27), with
calcareous sand, representing subaerial erosion, on the surface. North
of this point, a few feet, is a granite intrusive developed in some
magnitude on 204th Street, east of Post Avenue. It is a coarse granite,
flexed, and dislocated, much spotted and impregnated with tourmaline.
The
argument to raise the geological position of the Manhattan Island
rocks has been pursued with great earnestness by Dr. F. J. H. Merrill,
of the State Survey, and following the lines of research opened by
Professor Dana, he has, from stratigraphical (the relation of the rocks
in reference to the succession of beds) considerations, urged the
separation of the gneisses from the Highlands southward into three
groups (Borough of the Bronx), one overlying the limestone. The
limestone is made Calciferous-Trenton (see ante, Fig. 24), the Manhattan schists, Hudson River, and the Fordham and Yonkers gneisses archsean.
The limestone of Kingsbridge, as shown by Kemp, is a
