170 The American Geologist. March, 1891 
throughout. Its stratigraphic relation to a similar though thicker 
bed encountered in a deep well near Erie, Pa., is shown on 
plate iv.* 
Below this limestone, gray calcareous shales reappear, and con- 
tinue to a depth of 2670 feet, when they suddenly become very 
dark and fissile. This phase continues for about 45 feet when a 
second limestone appears. Nothing corresponding to this was 
noted in the Erie well ; but it apparenth* does have a representa- 
tive in a wellf at East Aurora, Erie Co., X. Y. , as shown in the 
plate just referred to. 
MARCELLUS GROUP. 
At a depth of 2725 feet, black shales reappear and continue for 
about 50 feet, to the upper surface of the Corniferous limestone. 
It is possible that all these shales do not belong to the Marcellus 
group, but that the}' are in part Hamilton. Again, the 45 foot 
bed of dark shale immediately overlying the limestone just de- 
scribed, appears in even* respect like a typical Marcellus deposit. 
UPPER HELDERBURG GROUP. 
The Corniferous limestone was found at a depth of 2775 feet. 
It seems to present no unusual features, being generally pure 
though sometimes siliceous, and vaiwing in color from a light to a 
dark shade of gray. Xo line of demarcation is observable by 
which this limestone can be separated from the Onondaga below. 
Their total thickness is about 150 feet. 
ONONDAGA SALT GROUP. 
This differs from the above, principally by the more frequent 
occurrence of argillaceous bands, and the greater diversity in 
texture and color of the limestone strata. The group was pene- 
trated to the depth of only 338 feet. 
II Stratigraphic Deductions. 
(A) Dip. — From the following localities and altitudes of the 
Corniferous limestone (upper surface), the amount and direction 
of its dip can be readily ascertained. 
Black Rock. Erie Co., X. Y +625 ft. A. T. 
Jamestown. X. Y.. 59.3 mis. S. 18° 10 W. of Black Rk— 1450 ft. A. T. 
Erie, Pa., 80 mis. S: 49° 30' W. of Black Rock -730 ft, A. T. 
*Compiled from manuscript notes kindly furnished by Mr. Charles S. 
Prosser. I", s. Geological Survey. 
lAlso from Mr. Prosser's notes. 
