12 ROCK FLOOR OF GREATER NEW YORK. [bull.270. 
REVIEW OF STRUCTURAL GEOLOGICAL STUDIES OF THE NEW 
YORK CITY AREA. 
330ROUGHS OF MANHATTAN AND THE BRONX. 
Gale. — The earliest geological work of importance treating of the 
geology of New York Island is a paper by Dr. L. D. Gale, dated 1839. 
As quoted by R. P. Stevens, Gale" describes the geological topography 
of the island as a " group of ' gncdssoid islands separated from each other 
by low levels slightly elevated above tide and filled with drift and allu- 
vium." It would be difficult even now to express better the peculiar- 
ities of the relief of the island. 
Gale's geological report, published in Mather's volume, on the 
Geology of the First District* is a careful description of outcrops 
examined along longitudinal sections of the island, corresponding in 
position with the principal avenues. This descriptive matter has much 
value as a record of exposures, many of which have since been pared 
away in grading the city. He says in resume: 
The general direction of the strata is N. 25° E. to N. 35° E. and corresponds with 
the direction of the avenues; and the dip, though generally to the west, averages 
within 10° of the vertical. 
Math. i'. Mather's report contains a geological map of Manhattan 
Island and in addition to the valuable section by Gale, above referred 
to, includes an important table giving a large number of dips and 
strikes, and a table of joint directions as well. c 
Cozzens. — Isaachar Cozzens published in 1st:; a little volume on the 
Geology of Manhattan Island' 7 which is chiefly valuable as a record of 
the character of exposures which are no longer accessible for study. 
Stevens. — In 18G5 appeared a valuable paper by Mr. R. P. Stevens, 
of the New York Lyceum of Natural History, in which paper the 
rock composition and the structure of the island were much more fully 
discussed than at any previous time/' The peculiar topographic 'devel- 
opment of the island was accounted for in part by folding, but more 
largely by faulting. His diagonal section across the northern end of 
the island shows five transverse folds in the gneiss and underlying 
limestone. The western and the eastern anticlines of the series he 
supposed brought up the limestone in the beds of Hudson and East 
rivers, respectively, thus accounting in part for the formation of 
these channels. He supposed another anticline to follow the gorge of 
the Harlem between Washington and Ford ham heights. The remain- 
ing two anticlines of his series he based upon the occurrences of lime- 
aStevens, R. P., Hist. Geol. New York Island: Annals Lyceum Nat. Hist. New York, vol. 8, L865, pp. 
108-120. 
bMather, Win. W., Geol. New York. pi. 1. 1843, pp. 581 604. 
cldem, pp. 605-625. 
dCozzens, Isaachar, Geol. New York, 1843, pp. l-n ), pis. I '.». 
