﻿S. V. Woodjim. — American and British Surf ace- Geology. 489 



waters in following the retreating glacier covered, and in part strati- 

 fied, the material ground up 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 somewhat 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 lias yet been detected in America of the return of 

 the glaciers to the area lohich they had before occupied and abandoned 

 after the intervention of a milder climate, such as is found in Europe. 

 Now the preservation of so considerable an extent of forest-grown 

 surface to the Erie clay, that is, between the deposits No. 1 and those 

 presently to be described under the symbol 3a, seems repugnant to 

 such an oscillation of climate ; because this surface, and indeed the 

 Erie clay itself, would, we must infer, have been ground out and 

 destroyed by any re-occupation of its former site by glacier-ice,^ 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 



^ 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, but I do not believe in the 

 possibility of such a thing, the two resulting actions appearing to me irreconcilable 

 with each other. According to Prof. Dana the thickness of the ice which passed 

 over the noi-thern part of the United States was 6000 feet, exerting a pressure of 

 300,000 lbs. to the square inch, while it was double this on the watershedbetween 

 Canada and Hudson's Bay. I am, however, very sceptical of these vast thicknesses 

 of ice anywhere. 



