254 Address before the Association of American Geologists. 
are abraded over all northern countries. Vast blocks of stone are 
likewise conveyed without abrasion, by the advance of a 
ciers, and lodged in peculiar situations. 
From year to year, the evidence has been increasing, of the 
prevalence of intense cold in northern regions in the period im- 
mediately preceding the historic. The elephants and rhinoceros 
found, undecayed, in the frozen mud.of Siberia, the arctic charae- 
ter of the few organic remains found in the post-tertiary strata of 
Scotland and Canada, and described by Lyell and Bowman, and 
of the borders of Lake Champlain, as described by Emmons 
and Conrad; and the great extension of the ancient moraines in 
the Alps, are the evidence from which Agassiz infers that in that 
period, all northern countries were covered with a vast sheet of ice, 
filling the valleys and extending southerly as far as diluvial phe- 
nomena have been observed. Glaciers would then be formed on 
‘mountains of moderate altitude ; and, indeed, he supposes that 
all the northern parts of the glohe might have constituted one 
vast Mer de Glace, which sent out its enormous glaciers to the 
south; thus giving the same direction to the drift and the strie 
on the rocks. As these vast masses of ice melted away, when 
the temperature was raised, immense currents of water wé 
the result, which would lift up and. bear away huge igebergs, 
whereby extensive erosions would. be produced, and_ blocks of 
stone be transported to great distances. . Subsequently, er 
would be formed where moraines had produced barriers, clay and 
sand would there be quietly deposited, and the waters be ultic 
mately drained by the wearing down of the barriers of detritus. 
-It is doing injustice to this theory to attempt so brief a descrip 
tion of it. A detailed account of existing glaciers, which cannot 
here be given, forms the best preparation for a just appreciation 
the theory. Admitting its truth in the main, let us see how i 
applies to the. phenomena of drift in this country. 
In the first place, it explains satisfactorily, the origin is those 
singular accumulations of gravel and bowlders, which we meet 
be sy ye ied fare northern ane of our country- - 
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