On the Geology of the Island of Aquidneck and the Neighboring Parts of the Shores of Narraganset Bay

Abstract

GLACIAL DEPOSITS AND ICE MARKS.-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 characteristic 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 deposits 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 ill 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 specimens came from more remote regions to the northward, but inasmuch 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 the drift mass is made up of boulders of a conglomerate, which