No. 275.] 
221 
nute proportion of lime which they contain, exhibiting the crystals along 
the edges. Wherever larger masses of pyrites occur, we find a propor- 
tionate increase in the quantity of sulphate of lime. Similar conditions 
in some of the limestones below have produced a mass of gypsum, fil- 
ling the cavity previously occupied by the pyrites; and analogous cir- 
cumstances, and varying in extent and effect, may have formed the vast 
gypsum beds of the same series, extending throughout the whole of 
Western New-York, The latter however could only have occurred be- 
fore the entire induration of the surrounding rocks. 
CHEMUNG COUNTY, 
In this county, the group last described forms the surface rocks of the 
northern towns; and in the ravines and valleys, extends south to the 
southern line of the towns of Veteran and Catlin, The rocks here re- 
tain most of their essential characteristics; but fossil shells are exceed- 
ingly rare, and in many localities entirely wanting. The peculiar fu- 
coidal markings are every where preserved in the thin layers of sand- 
stone. The rocks of this group are well developed in Gulf creek, near 
Jefferson, at the head of Seneca lake; and at many points south on the 
west branch of the valley, and the ravines coming into it. 
From Jefferson to Millport, the rocks dip south, exhibiting through- 
out continued alternations of shale and sandstone; and towards the up- 
per part the compact shale is covered with fragments of a Fucoid, dif- 
ferent from those below, and appearing only in curved fragments. 
In the vicinity of Millport, and farther south, the sandstone layers at* 
tain a thickness of a foot or more, and are quarried for works on the ca- 
nal and various other purposes; and at Pine valley, the sandy layers of 
the rock, are quarried in two places. Mr. Sexton, the owner of the 
last, informs me that the firmest layers of sandstone often pass into shale 
so as to be unfit for any economical purpose. This appears to be un- 
like the thinning out of the layer; but the proportion of argillaceous 
matter becomes so great that the mass crumbles on exposure. 
At the last named quarry, I observed the singular fact of non-con- 
formable strata, as yet the only instance noticed, and which various cir- 
cumstances seem to render incredible. The strata are parts of the same 
mass, once continuous, the lower dipping south at an angle of four or 
five degrees, and the upper dipping north at about the same angle; 
and a short distance farther south the whole mass dips north. The only 
explanation that now offers, is that at the time the rocks were sul^ected 
[ Assicra. No. 275. 1 41 
