A. Winchell on the Geology of Petroleum in Canada. 177 
, ‘ 
limestone, often described as a sandstone. In some of the wells 
several feet of dark bituminous shale are found occupying a 
variable position in the series. In some parts of the oil-produc- 
ing region the above series is overlaid by from 2 to 100 feet of 
black, hard, bituminous and somewhat calcareous shale. 
other parts this has been denuded, and in still others the Hamil- 
ton Series is found worn down to varying depths. 
The Black shale has been shown by me from stratigraphical 
data (Mich. Geol. Rep., 1860, p. 79; this Jour., [2], xxxiii, p. 
53; Ib., xxxix, p. 851) to be the western equivalent of the 
Genesee shale, though by some geologists referred to the Portage 
group, and by others to the Marcellus shale. More recently — 
in May, 1865,—I obtained a few fossils (embracing Discina Lo- 
densis, and Leiorhynchus multicosta) which perfectly establish the 
correctness of my former determinations. I know of no rocks 
of the age of the Portage group in Canada j : 
The series of rocks below the Black shale is unequivocally 
Hamilton, and identical with the series outcropping at various - 
laces in Canada West and Michigan. The buffish magnesian 
imestone is likewise found at the base of the Hamilton group in 
Little Traverse bay in Michigan. The entire thickness of the 
Hbegg group proper in the oil region of Canada West is about 
eet. 
m various depths in the rock. : 
Whether the supply originally ascended from the underlying 
