426 J. D. Dana—On Southern Westchester County 
I have made many additional observations which are here 
included. The facts will be found to explain the origin of some 
of the features of New York Island, and indeed of New York 
City, while illustrating also certain general stratigraphical fea-_ 
tures of the Green Mountain system. In order that the points | 
may be readily ihe le a large geological map of the area 
is here added. (See Plate XIX. 
Explanations of the ig —The accompanying map is drawn 
on a scale of one mile to two inches. For the sake of precision 
in locating observations, it has upon it the streets that have 
been laid out over the surface.* I have added also, from ony 
map has been copied, by permission, from one of the maps (Nos. 14, 15) 
of the xy A quarto Atlas of Westchester cou published by Messrs. J. B. 
Beers & Co., of New York. The original map of the Atlas is a third larger in 
scale, and gives, among its many details, the poncaarien of pr » cigarette aes of 
A 
Street, is about six and a quarter miles long out of the total thirteen and a half. 
But it contains less than one-third the whole area . oy ote” and but a small 
part of the population of the city. I here describe, of 
Supplement to the 2 Artie in the Number for No- 
RIV. ST.| vember last, a lim a not included i in the 
Ww 
— os the limestone, “e at q, q, quarries, 
the m rthern one on the Delafield estate. 
At k, ~ ts Minediindk and prs masses of lime- 
stone about the more southern appear to be partl 
77 high and abrupt declivity. About the northern 
AN 5 DUYVIL termination of the area, outcrops of schist occur 
IN near the river south of the Riverdale Station as 
and n 
the area to the — Liven! wert of N. 10°-18° E.; but north of the 
the strike of the schist changes to N. 34° E. The schist naomi th the area is 
ra nentdenilte, Some of the beds of limestone at both q contain 
