46 GEOLOGY OF OHIO. 
Second. That this agent must have been either water or ice. 
Third. That 1t was ice, because rivers never excavate such basins. 
In a plateau country, as this was, rivers could only produce narrow 
gorges, like the cafions of the Colorado, or shallower and broader valleys, 
widening towards their mouths, and with bottoms forming more or, less 
regular slopes. 
Fourth. That the ice was in the form of glaciers, and not icebergs, be- 
cause the lake basins, wherever they can be examined, are found to bear 
conspicuous marks of glacial action; the furrows and scratches having 
the bearing of the long diameter of each, and flint nodules, with ridges 
in their lea, and other signs, proving conclusively that the motion in 
Iiake Erie was from Buffalo toward Toledo. | 
Since the publication of our second volume, the subject of the origin 
of the great lakes has been discussed in a paper read by Prof. E. W. 
Claypole before the Natural History Society at Cincinnati, and published 
in the Canadian Naturalist, of April 6th, 1877. The theory advanced 
by the author of this paper is, that the chain of great lakes are only | 
portions of the valley of the pre-glacial river, to which reference has 
been made, blocked up in the ice period by beds of Drift. 
The considerations which oppose this theory are so apparent and for- 
midable, that it never could have been proposed or accepted by any one 
who had carefully studied the problem. In addition to those already 
suggested, they are— 
First. That the lakes occupy a series of boat-shaped rock basins, which 
have almost nothing in common with river valleys. The notion that 
the valley of a river could be beaded in this way by the broad excava- 
tion of such portions as lay in soft rock, and the formation of cafions 
through hard strata, has no warrant in any facts yet observed on the 
earth’s surface. : 
Second. The great and unequal depth of the lake basins renders it 
impossible that they could have been excavated by a continuous flow- 
ing stream. Lake Michigan is nine hundred feet deep to the silt which 
covers its bottom; it is excavated in rocks that are not softer than those 
of the adjacent country ; is surrounded by a rocky rim, from which, it is 
true, a narrow, buried channel leads, but that has, so far as known, no 
greater depth than two hundred feet—the depth of the pre-glacial river 
which drained this region before the formation of the lake. 
Lake Huron is eight hundred feet in depth, while the buried channel, 
which connects it with Lake Erie, is not more than two hundred feet 
deep. 
Lake Erie is generally very shallow, and while its bed is no doubt 
