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[Assembly 
the limestone region, and none of them of the character of those in Al- 
bany and Schoharie counties where the rock contains a greater thick- 
ness. 
Marcellus Shales. — The Onondaga limestone is succeeded by the 
" Marcellus shales," the Seneca limestone being absent. These shales 
possess their usual essential characters, the middle portions quite com- 
pact and highly bituminous, becoming more slaty above and below. — 
The compact part of the shale usually contains large septaria ; these 
sometimes consist of large silico-argillaceous masses without seams of 
crystalline matter. This rock follows the same course as the hmestone, 
commencing on the east near the north line of the county, it passes south- 
west to the Genesee river ; thence its course is northwest though the 
town of Caledonia, passing into Genesee county near the north line of 
this town. 
On the Conesus outlet near the lower saw-mill at Avon, this shale 
may be seen resting on the limestone. About thirty-five feet from the 
bottom of the shale there is a stratum of limestone one foot thick, some- 
times concretionary, and containing Orthocera, fragments of trilobites &c. 
For several feet below this, the rock is black, slaty and very fragile. A 
few feet of the shale above this limestone is black and slaty ; it abounds 
in fossils of Orthocera, Orthis, Leptaena, Pterinea and a very small 
species of Orbicula. Above this the mass graduates into a greyish or 
bluish grey slaty shale, and contains few fossils. 
This shale is seen in the ravines and hill-sides, on the west side of 
the Genesee, extending through the northeast corner of York, and thence 
through the southwest part of Caledonia. Mr. Hallenbeck of Mum- 
ford accompanied me to a place in the south part of this towji, where a 
digging for coal had been made in the black shale. The indications 
which induced digging at this place were the black and highly bitumi- 
nous character of the shale, thin seams of coaly matter and petroleum. 
I did not learn to what depth the excavation extended, but presume it 
to have been less than forty feet, for at that depth the Onondaga lime- 
stone would have been reached. The excavations were made at two 
places, one on each side of a small shallow valley which was originally 
worn in this shale. North of the valley, on the farm of Mr. McLean 
the same shale was penetrated in digging a well. Some portions of 
the rock are so highly charged with bitumen as to burn when thrown 
into a hot fire. In these shales as well as in the upper black shale, 
