ON THE GEOLOGY OF THE ISLAND OF AQUIDNECK 
AND THE NEIGHBORING PARTS OF THE 
SHORES OF NARRAGANSET BAY.* 
[Concluded from page 528.] 
BY PROF. N. S. SHALER. 
Gracia, Deposits AnD Ice Marxs.—The contour of a surface 
alone is generally sufficient to establish the. former existence of 
glaciers, if they have ever worked upon it, but it is not to these 
indications alone that we must look for the evidence of the work 
of this great agent in this region. Every mass of rock exposed 
to view shows the rounded, smoothed and scored surface so char- 
acteristic of ice work. Every part of the island, level enough to 
carry such material, is buried beneath a coating of detrital material 
from two to forty feet in thickness. We propose to study these de- 
posits of glaciated matter with a view to determine some of the more 
important features connected with the work done by moving ice. 
These deposits have a composition which varies considerably 
according to the position in which they are found. At the extreme 
northern end of the island, all the pebbles found in them are from 
rocks which belong beyond its limits. The greater part of the 
pebbles can be referred to rocks which are in place on the shores of 
Mount Hope Bay to the northward, though some seem to come 
from points as far up as the neighborhood of Taunton. Only a 
small part cannot be readily referred to materials in place in the 
basins of the streams which flow into Narraganset Bay. It is of 
course impossible to assert that none of these unreferred spec- 
mens came from more remote regions to the northward, but inas- 
much as there is a very wide difference noticeable between the 
glacial material in the basin of the Charles River and the other 
streams which flow into Massachusetts Bay, and this drift on the 
north of Aquidneck island, there can be little doubt that the 
transportation of erratics, from limits more than fifty miles away, 
has been very slight indeed, if it occurs at all. A large part of 
. 
drift mass is made up of boulders of a conglomerate, which 
: Thi ONYE z s de to Prof. Benj. Pierce, Superintendent of the 
nited States Coast Survey, and is published by his permission. (611) 
