_ Limestone Belts of Westchester County, N. Y. 453 
Passing south from Hortentown over Archean rocks for 
fifteen miles (in a direct line) the first of the l'mestone outcrops 
up Peekskill Hollow is reached; and the rock where most 
-erystalline is undistinguishable from the white fine-grained 
limestone of East Fishkill ; moreover, it is accompanied by a 
well-bedded quartzyte, which affords good slabs for the floors 
of furnaces. The limestone may have once—before denuda- 
tion began its long work-—extended farther northward toward 
Dutchess County. But whether so or not, the similarity of the 
limestones of the two regions, and especially the similar associa- 
tion with quartzyte, add weight to the argument for sameness 
of geological age. Like the quartzyte of Dutchess County, 
that to the south is, in all probability, the Potsdam sandstone ; 
and as the limestones of Dutchess County include beds of 
the Calciferous as well as the Trenton, as proved by fossils, so 
the limestones of Westcl:ester County may have the same range; 
or, if not the whole, may cover at least the earlier part of the 
Lower Silurian. This true, the conformably associated schists 
of Westchester County are Lower Silurian in age, whatever 
their coarseness of crystallization, whether mica schist, gneiss, 
or anything else. 
survey of that State.* For the small northern portion about 
Newburgh, I am indebted to Professor W. B. Dwight of 
Poughkeepsie. Its areas are explained underneath the title. 
The part between the Hudson River and the Archean which is 
left in black is Triassic. 
once obvious that the slates and limestones of Dutchess County 
are continued southwestward in those west of the Hudson. 
his is so lithologically. More than this, it is so strati- 
graphically and paleontologically ; for Lower Silurian fossils like 
th ounty have been found in both the slates 
a mile south of Washington Lake (the lake in which the New- 
burgh limestone terminates), the gritty beds of the slate crowded 
be Saiear. of N 
& geological Atlas. Newark, 1868. : uate 
. Nelson Dale, this Journ., xvii, 59, 1879; W. B. Dwight, ibid., xix, 50, 451, 
1880; R. P. Whitfield, ibid., xviii, 227, 1879. 
Am. Jour. Sci.—Tuirp SEriEs, Vou. XX, No, 120,—Dzc,, 1880, 
29 
