﻿GEOLOGY OF THOUSAND ISLANDS REGION 137 



the rubbing and grinding action of a continental ice sheet has long 

 been recognized, and now it seems almost certain that instead of 

 only one there have been several ice invasions of the territory. 

 Students of glaciation find evidences of multiple glaciation in the 

 Mississippi basin, in Canada, in New England and in Pennsylvania. 

 It seems impossible that New York should have escaped occupa- 

 tion by ice sheets that buried surrounding territory. In the Mis- 

 sissippi basin the glacial epochs have been named as follows, in 

 order of time: Jerseyan, Kansan, Illinoian, Iowan, early Wisconsin 

 and later Wisconsin. While there is some doubt as to the validity 

 of the Iowan yet the multiplicity of the glacial invasions seems 

 to be a fact. The intervals between the glacial stages, the inter- 

 glacial epochs, are believed to have been long periods of temperate 

 climate. It seems possible that our present time of release from 

 glacial conditions may be only a warm interval between the latest 

 ice invasion and another invasion to come in the near (geologi- 

 cally) future. 



This matter of multiplicity of ice invasions is here emphasized 

 for the reason that the glacial features of our district seem to re- 

 quire for satisfactory explanation the work of more than a single 

 ice sheet. The glacial phenomena will be described in proper order. 



Submergence. Lake Iroquois. As the latest glacier waned 

 and the front receded and moved northward the ice was replaced 

 by a body of water, the glacial lake Iroquois. This great lake, held 

 in the Ontario basin by the ice barrier blocking the St Lawrence 

 valley, and with its outlet at Rome to the Mohawk-Hudson, laved 

 the receding ice front continuously over all the area described in 

 this paper. An important effect of this condition, which the reader 

 should hold in mind, is that all the materials left by the waning 

 ice were laid down beneath the Iroquois waters, and are conse- 

 quently more or less modified by the water action. 



The present altitude of , the Iroquois beach east of Watertown is 

 733 feet. The only point on the entire area covered in this paper 

 which is sufficiently elevated to reach the Iroquois plane is the ex- 

 treme southeast corner of the area, as shown, at the bottom of the 

 Theresa sheet, [pi. 44]. Here the nose of the Rutland promontory 

 brings the 800 foot contour on the map and the Iroquois shore line 

 is a steep cliff on the limestone scarp. On account of the postglacial 

 uplift and northward tilting of the region the Iroquois plane, and all 

 later water planes, rise to the north. On the parallel of Redwood 

 it is estimated that the Iroquois water surface was about 800 feet, 

 and at Chippewa Bay toward 900 feet. The depth of water over 



