MARCELLUS shale. 
179 
stitute a continuous stratum, assumed this form. The continuous stratum of limestone before 
noticed appears at this place, having the same character as elsewhere. The shale above it is 
very fissile, separating into thin laminae, and abounding in fossils. 
The lower part of the mass, on weathering, becomes iron-stained; but that portion above 
the limestone weathers to an ashen hue. 
A little west of the village, the shale approaches the surface so nearly that it blackens the 
soil along the road. 
West of Le Roy, there are few good points where this rock can be seen. The great depth 
of alluvion about the point of its junction with the Corniferous limestone has generally obscured 
the lower portion. At Alden and a few other points in Erie county, the upper part of the 
slate, abounding in Tentaculites, can be seen. The deep excavation along the valleys of 
Cayuga and Seneca creeks near Buffalo, and the depth of the drift and alluvion, effectually 
conceal this rock, though the Hamilton group above is well exposed. 
Localities. — The two principal localities in the district, and those to which an observer 
should direct his attention, are the ravine of Conesus outlet, a little west of the village of Avon ; 
and the bed and banks of Allen’s creek, near Le Roy. At the former place, the absolute 
contact of the Marcellus shale with the limestone below is seen beneath a sawmill, where the 
rock is exposed. Its extent upwards is well exhibited, and its peculiar fossils can all be ob¬ 
tained. At Le Roy the same features are exhibited, and its connexion with the limestone is 
distinctly seen. 
There are no other localities in the district, where the connexion with the lower rocks, and 
the characters of this, are so well exhibited. 
Thickness. — The greatest thickness of this rock, where it can be measured accurately, 
does not amount to more than fifty feet; but as before stated, it gradually merges into the 
olive shales above. In the Third District, this shale is much thicker. 
Minerals. — This rock contains no minerals of importance. Sulphuret of iron is every¬ 
where found. Sulphate of baryta often occurs in the septaria, and crystallized carbonate of 
lime in the same situation, and lining the cavities of fossil bodies. 
Springs. — From the presence of iron pyrites, the water flowing over, or rising from fis¬ 
sures in this rock, is often charged with sulphuretted hydrogen, though there are no copious 
springs. 
Agricultural characters. — The shale alone, on decomposing, produces a clayey soil; but 
its width being small, and the accumulation of drift at this point being excessive, it rarely gives 
character to the surface soil for any considerable extent. 
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