(Review of (Recent Literature. 63 
tain it. It was formed at or about the time that these strata were de- 
posited. 
In order that there may be a supply of gas or oil from any drilled 
well it is necessary that three geological facts must co-exist at that place, 
(i) A producing source of oil or gas in the form of a sti-atum charged 
with organic matter. (2) An overlying reservoir in the form of a 
porous sandstone or limestone, and (3) an iinpervious, fine-grained rock 
or cover. A fourth element seems also necessary, at least in the high- 
pressure wells; viz., an anticlinal fold in the underlying strata, as pointed 
out by Prof. I. C. White. 
At Findlay the gas is essentially light carburetted hydrogen, or marsh 
gas, but with small quantities of hydrogen and nitrogen, and its heating 
quality greatly exceeds that of the present Pittsburg supply. Its natural 
pressure is about 375 lbs. to the square inch. In the spring of 1886 there 
was a daily waste, for several months, of at least 16,000,000 cubic feet of 
gas at the Findlay wells. The flow of gas sometimes diminishes and is 
then accompanied, especially at Lima, by petroleum, or by petroleum 
and brine. 
The lake-age in Ohio; or some episodes during the retreat of the 
North American ice-sheet. By Prof. E. W. Cx-AYPgle, of Buchtel Col- 
lege, Akron, O. (Mc Lachlan & Co., Edinburgh; Robert Clark & Co., 
Cincinnati.) The former existence of a great ice-sheet over the midland 
region of North America has now passed beyond the domain of specula- 
tion and is one of the admitted facts in American geology. The above 
named paper is an attempt to trace the series of changes which must 
have followed the retreating ice. It is divided into three parts, the first 
of which considers the condition of the Ohio and the adjacent country 
at the time of the greatest extension of the glacier. The various lines 
of evidence brought forward during recent years are considered and the 
inferential geographical changes are detailed. In the author's opinion 
the valley of the Ohio was occupied for many years by a great body of 
water, "lake Ohio," the approximate outline of which is traced and its 
probable history sketched. The causes and the mode of its disappear- 
ance are touched upon and the traces which it left upon the country are 
stated. 
The second stage in the story commences when the retreat of the ice 
had carried it so far north that the whole southern portion of Ohio was 
uncovered and the ice-front had receded to the northern slope of the 
water-shed of the state. When it occupied this position it completely 
blocked the outflow of all the rivers flowing in that direction. There 
were consequently formed a multitude of little glacial lakes or ponds 
held in by the ice until they overflowed to the southward, forming as 
many streams whose waters ultimately found their way into the Ohio 
river. The life history of one of these lakelets is traced in full as an ex- 
ample of what the others must have been. This is "lake Cuyahoga," 
formed in the valley of that river between Akron and Cleveland. The 
overflow of this was through the gap in which Summit lake and the 
