368 POPULAR SCIENCE MONTHLY. 



the large glacial Lake Algonquin, succeeding the larger Lake 

 Warren, and by the eastward and northeastward surface atmos- 

 pheric currents and courses of all storms, was not less mild than 

 now. The trees whose wood is found in the interglacial Toronto 

 beds now have their most northern limits in the same region. 



Somewhat later came the full expansion of the glacial Lake 

 Iroquois, in the basin of the present Lake Ontario and northward, 

 outflowing at Rome, N. Y., to the Mohawk and Hudson rivers. 

 Gradual re-elevation of the Rome outlet from the Champlain 

 subsidence had lifted the surface of Lake Iroquois in its western 

 part from near the level of the present lake at Toronto to a height 

 there of about two hundred feet, finally holding this height during 

 many years, with the formation of the well-developed Iroquois 

 beach. 



The final stage in the departure of the ice sheet which we are 

 able to determine from the history of the Laurentian lakes and 

 St. Lawrence Valley, was when the glacial lake St. Lawrence, out- 

 flowing through the Champlain basin to the Hudson, stretched 

 from a strait originally one hundred and fifty feet deep over the 

 Thousand Islands, at the mouth of Lake Ontario, and from the 

 vicinity of Pembroke, on the Ottawa River, easterly to Quebec 

 or beyond. As soon as the ice barrier was melted through, the 

 sea entered these depressed St. Lawrence, Champlain, and Ottawa 

 valleys ; and subsequent epeirogenic uplifting has raised them to 

 their present slight altitude above the sea level. 



Further stages of the glacier recession are doubtless recogniz- 

 able by moraines and other evidences, the North American ice 

 sheet becoming at last, as it probably also had been in its begin- 

 nings, divided into three parts — one upon Labrador, another 

 northwest of Hudson Bay, as shown by Tyrrell's observations, 

 and a third upon the northern part of British Columbia. From 

 my studies of the glacial lake Agassiz, whose duration was prob- 

 ably only about one thousand years, the whole Champlain epoch 

 of land depression, the departure of the ice sheet because of the 

 warm climate so -restored, and most of the re-elevation of the un- 

 burdened lands, appear to have required only a few (perhaps four 

 or five) thousand years, ending about five thousand years ago. 

 These late divisions of the Glacial period were far shorter than 

 its Kansan, Aftonian, and lowan stages; and the ratio of the 

 Glacial and Champlain epochs may have been approximately as 

 ten to one. The term Champlain conveniently designates the 

 short, final part of the Ice age, when the land depression caused 

 rapid though wavering retreat of the ice border, with more vigor- 

 ous glacial currents on account of the marginal melting and 

 increased steepness of the ice front, favoring the accumulation of 

 many retreatal moraines of knolly and bowldery drift. 



