614 ON THE GEOLOGY OF THE ISLAND OF AQUIDNECK. 
power as is’ possessed by the far thicker continental glacier. 
This last named form of the action can only take up masses 
material from the base over which it grinds; its ability to rend 
fragments from the rock beneath it would always be far greater 
than the stream glacier, on account of its superior thickness and 
therefore far greater crushing 
Examination of the materials deposited by these two forms of ice 
action shows us enough difference between them to enable us to 
determine to which of the two any given mass of glacial material 
belongs. Where alarge part of the fragments are angular, showing 
no trace of grinding against the bottom of the glacier, we may 
assume that the ice which carried the material was a local stream 
which received the mass of its load from that part of the sides 
of the valley in which it flowed which were above the level of the 
ice; where on the contrary the whole of the débris is more or less 
rounded, a large part polished or scored, and all showing the effect 
of the abrasion which must occur when the fragments are dr 
from their bed by the moving ice, we must conclude that the sheet 
had no side barriers from which a supply of débris could be fur- 
nished by falls and avalanches, as the existing glaciers in Swit- 
zerland are fed, but obtained their whole load from the bed w 
I am well convinced that all the débris on the island of Aquid- a 
neck has been deposited by ice acting in the last of these two 3 
methods. Possibly there may have been a little action of a more : 
local character, but the evidence forces us to the conclusion that a 
the principal part of the drift found here has been deposi" * 
the melting of a mass of ice in which it was held, rather er < 
transported renders it the more likely that all the material pi 
local origin. Rock masses resting on the surface of a ore 
in a position favorable for transportation to the greatest pace 
that the stream can flow; not so the detritus which rests 
the mass of ice and the bed rock. All the material torn "P 
its bed by the glaciers must remain permanently near to the ist 
relative level in the ice mass, close to its base, for be ne 
possible means whereby they could become lifted into be action 
parts of ice. Here they would be exposed to the wearing "4 
which results from continual grinding against the ee ead 
stream or constant friction against each other; this m 
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