114 History of the Geology of New York Island. 



Present History of the Geology of New York Island. 



Since the publication of the work of Mr. Cozzens, there has 

 not appeared any contribution to the geological knowledge of 

 New York Island. The artificial sections of its rock have been 

 largely increased in number, by the opening of new streets and 

 avenues, and the improvements' at the Central Park. Proba- 

 bly there is not another spot on the face of the globe where, in 

 so easy and accessible a manner, such numerous sections of 

 gneissoid and metamorphic rocks can be seen, as on the upper 

 end of our Island. We have, as roughly calculated, from 75 

 to 100 miles of artificial, and at least twenty miles of natural 

 sections. 



The artificial sections throw new light upon the structure of 

 the rock mass, and will be alluded to in this report. 



Our rocks are a portion of the main land in Westchester Co., 

 from which we are cut off by a profound fault, a cross fracture 

 in part, originally narrow, but widened by the abrading power 

 of water and ice, gravel and boulders, and, in part, by rupture 

 of the strata longitudinally, with subsequent abrasion. 



Beginning, on the North River, at Spuyten-Duyvel Bridge, 

 the first cross-fracture extends S.S.E. 1500 feet ; then com- 

 mences a longitudinal fracture extending to Tubby Hook, the 

 Spuyten-Duyvel Creek flowing in it 2000 feet. Another cross- 

 fracture then commences, extending to the Harlem River, in 

 which the creek flows 1000 feet, then it enters another longi- 

 tudinal fracture, in which it flows N.N.E. 4000 feet, where it 

 meets with another cross-fracture for 2000 feet. From thence 

 a longitudinal fracture extends as far southwards as McComb's 

 ' Dam and Bridge, running parallel with the North River ; from 

 thence the fracture slightly inclines south-eastwards to Hurl- 

 gate on the East River. 



At Tubby Hook there is another cross-fracture, extending 

 from the North River into the second longitudinal one. At Man- 

 hattanville there is another reaching across the entire island. 



Between the islands in the East River, and the New York 



