TOMPKINS COUNTY. 
477 
marks, and having the faces smooth and plain. Numerous alternations of this kind have been 
noticed through many hundred feet. Fossils rarely accompany the rippled layers, but are 
invariably found with the smooth. The materials of the two differ very slightly in mineral 
composition, the rippled ones being more sandy. So far as I have observed in this and other 
localities, the greatest accumulation of fossils is always accompanied by the fewest ripple- 
marks. 
In numerous localities of these rocks, the edges of strata, when exposed in ravines and 
other places, are found covered with crystals of sulphate of lime. This circumstance is by 
no means universal among the shales below, although observed in some localities ; while in 
the present group there are few exceptions. Pyrites, in minute particles, is every where 
disseminated, decomposing on exposure, and hastening the destruction of the rocks; while 
the sulphuric acid combines with the minute proportion of lime which they contain, exhibiting 
the crystals along their edges. Wherever larger masses of pyrites occur, we find a proportionate 
increase in the quantity of sulphate of lime. Similar conditions in some of the limestones 
below have produced a mass of gypsum, filling the cavity previously occupied by the pyrites ; 
and analogous circumstances, 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 before the entire induration of the surrounding rocks. 
The thin-bedded sandstones of this county afford some of the finest flagging stones observed 
in this part of the district. These are quarried in large slabs, having a thickness of from three 
to five or six inches. The thicker layers furnish a good material for buildings and foundations. 
There are several deposits of marl in the marshy ground at the head of Cayuga lake, which 
might be advantageously used for burning into lime. In the south part of the town of Hec¬ 
tor, there is an extensive deposit which is already largely used for burning into lime. There 
is another deposit in the same valley at Reynoldsville. 
About six miles south of Ithaca there is an extensive bed, and several small ones near 
Newfield. 
CHEMUNG COUNTY. 
The surface of this county is occupied by a series of broad high hills and deep narrow 
valleys; the Chemung valley is an exception, however, being broad and deep, with an exten¬ 
sive alluvial bottom. 
In the deep ravines of the northern part of the county, the rocks of the Portage group are 
exposed; but nearly all the surface is occupied by the Chemung group, the characters of 
which are already described. The rocks are deeply indented by numerous ravines which 
expose the strata to great advantage, and offer facilities for exploring their fossil productions. 
