ALLEGANY COUNTY. 
485 
places containing pyrites which stains the rock an iron-rust color. This sandstone is quarried 
in blocks from one to three feet thick, and of any required size ; it breaks easily when first 
quarried, and will scarcely stand the vicissitudes of climate. 
The tunnel at Portage is excavated in this rock, and the bank of the river above exposes 
it for one hundred and fifty feet, where it is cut for the passage of the canal; and again it 
appears at the north end of the bridge at Portageville. At these places large quantities of the 
rock have been quarried and dressed in blocks of various sizes for use on the locks, aqueducts, 
etc. of the Genesee Valley canal. At two or three other places within three miles south from 
Portage, the same rock is quarried in the shallow ravines along the valley of the Genesee 
river. 
Succeeding the black micaceous shale, are the sandstones and shales constituting the Che¬ 
mung group, which is every where visible in the ravines and banks of streams. Its northern 
limit extends through the south part of the towns of Centreville, Hume, Grove and Burns, 
and its characters are better developed in the next range of towns. In this county, more par¬ 
ticularly along the Genesee river and west, the group differs in lithological characters, and 
consequently in some degree in fossils, from the same rocks in Steuben and Chemung ; the 
latter containing more sandstone, and the shale having an admixture of siliceous matter, that 
renders the whole harsh to the touch. In the ravines along the Genesee river, a much larger 
portion is pure aluminous shale, of a deep green or bluish-green color; in this, at intervals, 
there are courses of nearly pure sandstone ; sometimes a single layer of a few inches, at other 
times several, forming a mass of four to ten feet thick. 
A very good exhibition of this group, and better than is elsewhere seen, in Allegany county } 
is on the Caneadea, from Rushford, near M‘Call’$ mills, to the mouth of the creek. The 
rocks consist of numerous alternations of shale and sandstone, the latter, often in layers of two 
or three inches, and other thicker ones, which are quarried for lockstones, building stones, and 
grindstones. One stratum of this sandstone, containing several courses of variable thickness^ 
affords a good material for grindstones, for which it is quarried on the land of Mr. Bannister. 
I did not learn the amount annually taken from this quarry, but judgin gfrom the numerous and 
distant points where the “ Rushford grindstones” are sold, it is greater than any other in the 
district. 
Rocks similar to the last, but none of the same strata, are seen in Black creek, Crawford’s 
creek and White creek. In the banks of Black creek, at Rockville, some thick masses of 
sandstone alternate with green shale, which is slightly calcareous and contains abundance of 
fossils. Two of the sandstone strata are about six feet thick each, and divided into courses of 
from two to three feet. Similar sandstone is quarried half a mile southwest, on the line of 
the canal; it contains fossils of Atrypa and Deltyris ; and a mile and a half south, and sixty 
feet higher than the last, a sandstone is exposed on a bank of a small stream. The layers are 
thin, but extremely siliceous and durable. 
The rocks at Rockville are all highly bituminous, the sandstone so much so that it scents the 
clothes of the workmen ; and the water of the springs, though clear, has the taste of bitumen. 
