r.22' The American Geologist.. February,, i899 
INTRUSIVES IN THE INWOOD LIMESTONE OF 
MANHATTAN ISLAND. 
By E. C. Eckel, New York. 
(Plate III.) 
The rocks of southeastern New York, according to Prof. 
C. R. Van Hise and Dr. F. J. H. Merrill, may be classified as 
follows : 
Ordovician: 
1. Manhattan schist — mica schist containing garnet, fibrolite, ky- 
anite, and staurolite. Hudson River age. 
2. Inwood limestone— crystalline dolomyte, containing diopside and 
tremolite. Calciferous -Trenton age. 
Cambrian. 
I. Lowerre quartzyte. 
Precambrian. 
1. Fordham gneiss; Algonkian? 
2. Granites and gneisses; Archjean? 
At a time beginning not later than the Upper Silurian, and 
possibly continuing at intervals to the end of the Palaeozoic 
(F. J. H. Merrill), these strata were thrown into parallel folds 
having a general northeasterly trend. Transverse folding has 
resulted in a general gentle pitch to the southwest, and over- 
thrown folds are common. 
Of the formations mentioned above, the Manhattan schist 
and Inwood limestone form the surface or subsurface strata 
over the greater part of Manhattan island, though at one place 
a small extent of the Fordham gneiss is exposed. The Man- 
hattan schist is everywhere cut by sheets and dikes of peg- 
matyte, but no intrusive has heretofore been described from 
the Inwood limestone of Manhattan island. The purpose of 
this paper is to describe one locality on the island at which 
such an intrtision is a ver}^ striking feature of the section. 
This occurs at Hawthorne street, between Nagle and Sherman 
avenues, a few blocks north of Fort George. 
At this point the cutting for Hawthorne street has exposed, 
on both sides of the street, rock-sections twenty to thirty feet 
in hight and about seven hundred feet long. The entire sec- 
tion consists of the Inwood limestone and its contained intru- 
sives. At the southerly corner of the east side of the street, 
however, gneiss is exposed. Continuing south toward the 
Harlem river, after an intervening drift covered surface, the 
gneiss is again met, and then limestone again becomes the sur- 
face rock. The relations of the gneiss and limestone will be 
recurred to later. 
