206 SURFACE GEOLOGY. 
long journeys from the North; in fact, as some sort of huge 
terminal and lateral moraines. I have, however, disproved, 
as I think, this theory of their transportation in a paper pub- 
lished some years since (Notes on the Surface Geology of 
the Basin of the Great Lakes. Proc. Bost. Nat. Hist. Soc. 
1863), in which it is urged that the continuous sheet of the 
Erie elays upon which they rest, and which forms an un- 
broken belt between them and their place of origin, pre- 
cludes the idea that they have been transported by any ice- 
current or rush of water moving over the glacial surface; as 
either of these must have torn up and scattered the soft clays 
below. 
There is, indeed, no other conclusion deducible from the 
facts than that these sands, gravels, granite and greenstone 
boulders— masses of native copper, etc., which compose the 
superficial Drift deposits — have been floated to their resting- 
places, and that the floating agent has been ice, in the form 
of icebergs; in short, that these materials have been trans- 
ported and scattered over the bottom and along the south 
shore of our ancient inland sea, just as similar materials are 
now being scattered over the banks and shores of Newfound- 
land. ; 
If we restore in imagination this inland sea, which we 
have proved once filled the basin ot the lakes, gradually dis- 
placing the retreating glaciers, we are inevitably led to a 
time in the history of this region when the southern shore 
of this sea was formed by the highlands of Ohio, etc., the 
northern shore a wall of ice resting on the hills of crystalline 
and trappean rocks about Lake Superior and Lake Huron. 
From this ice-wall masses must from time to time have 
been detached,— just as they are now detached from the 
Humboldt Glacier, — and floated off southward with the cur- 
rent, bearing in their grasp sand, gravel, and boulders— 
whatever composed the beach from which they sailed. Five 
hundred miles south they grounded upon the southern shore ; 
the highlands of now Western New York, Pennsylvania and 
