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[Assembly 
before described, that these rocks are fully developed, and may be 
seen in perpendicular cliffs, from 200 to 350 feet high. The same 
rocks are traced along the Genesee valley for several miles, when they 
are succeeded by the olive shaly sandstone and black micaceous shale, 
which occupy a part of the towns of Eagle, Pike, Centreville, Burns 
and Portage. The thin layers of sandstone interstratified with the 
black shale, and also those usually succeeding it, are quarried on the 
Wiscoy a mile west of Pike Centre, near Pike Hollow, and at many 
other places along the outcrop and in the ravines and valley sides. 
The upper part of the Portage group consists of a mass of slightly 
argillaceous sandstone, compact and fined grained, from 150 to 200 
feet thick ; in some 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 quar- 
ried, but becomes very firm when exposed to the vicissitudes of chmate. 
The Tunnel, at Portage, is excavated in this rock, and the bank of 
the river above exposes it for 150 feet, where it is cut for the passage 
of the canal ; and again it appears at the west end of the bridge at Por- 
tageville. At these places large quantities of the rock are quarried and 
dressed in blocks of various sizes for use on the locks, aqueducts, &c. 
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. 
The requisition for stone along the line of the Genesee Valley canal 
has greatly increased the value of good quarries, and even indifferent 
ones yield a large profit. 
Succeeding the black micaceous shale, are the sandstones and shales 
constituting the Chemung group, which is every where visible in the 
ravines and banks of streams. Its northern limit extends through the 
southern 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 particularly along the Genesee river and west, the 
group differs in lithological characters, and consequently in some de- 
gree in fossils, from the same rocks in Steuben and Chemung ; the 
latter containing the 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 alumi- 
nous shale, of a deep green or bluish green color; in this, at inter- 
