S. V. Woocljun. — American and British Surface- Geolog y. 489 
waters in following the retreating glacier covered, and in part strati- 
fied, the material ground np by it. In this view he (as do also 
several American geologists) differs from Principal Dawson, who 
has attributed the glaciation of the Atlantic coast to an Arctic 
current carrying icebergs, instead of to glacier-ice, either solely or 
in connexion with a following sea. It seems to me, however, as 
explained presently, that though formed in the way Prof. Newberry 
contends, they are more probably synchronous with the beds 3a, 
presently described, or even to some extent with the Lake terraces, 
or beds No. 4. 
2. The formation which immediately succeeds the Erie clay in 
Ohio is, according to Prof. Newberry, that of a terrestrial surface 
indicated by forest-beds with logs and stumps, and sometimes up- 
right trees, of which beds he gives many instances. This formation 
(No. 2), or the deposits associated with it, contains the bones of 
Elephant, Mastodon, and the giant Beaver, and it indicates, accord- 
ing to the Professor, a climate somevvhat colder than that now 
prevailing in the same region, though some of the forest-remains of 
Ohio contain a large number of plants still growing there. 
With reference to this terrestrial surface, Prof. Newberry observes 
that no certain proof has yet been detected in America of the return of 
the glaciers to the area which they had before occnpied and abandoned 
after the intervention of a milder climate, such as is found in Europe. 
Now the presei'vation of so considerable an extent of forest-grown 
surface to the Erie clay, that is, between the deposits No. 1 and tliose 
presently to be described ipider the symbol 3«, seems repugnant to 
such an oscillation of climate ; because this surface, and indeed the 
Erie clay itself, would, we must infer, liave been ground out and 
destroyed by any re-occupation of its former site by glacier-ice, 1 and 
in such case the deposits which succeed it would all appear to 
belong to that period which, having followed the retreat of the con- 
fluent glacier-sheet in Britain and the elevation of this country from 
its general submergence, English geologists have hitherto been 
accustomed to call post-Glacial. 
If, however, Prof. Newberry is right in regarding the glaciation 
which gave rise to the Erie clay as having taken place when Ohio 
stood 500 feet and more above its present level, and the beds which 
succeed the forest-surface as having been accumulated when the 
same area was depressed to as great or even greater depth below that 
level, this difference of altitude (1000 feet) may have so reduced the 
second glaciation as to prevent the re-occupation of the Erie clay 
area in Ohio by glacier-ice, notwithstanding the return over the earth 
1 This, as described further on in the present paper, has been the case with the 
Lower Glacial deposits in England. Mr. Geikie seems to see no difficulty in glacier- 
ice passing over forest-surfaces without destroying them, although to such ice is 
attributed the excavation of great valleys and rock-basins, hut I do not believe in the 
possibility of such a thing, the two resülting actions appearing to me irreconcilable 
with each other. According to Prof. Dana the thickness of the ice which passed 
over the northern part of the United States was 6000 feet, exerting a pressure of 
300,000 lbs. to the square iuch, while it was double this on the watershed between 
Canada and Hudson’s Bay. I am, however, very sceptical of these vast thicknesses 
of ice anywhere. 
