312 ANNUAL BEPOBT SMITHSONIAN INSTITUTION, 1912. 



doned. Following tMs the lake level fell as the ice withdrew, until 

 the sea, which then stood relatively higher than now (523 feet higher 

 near Covey Hill, on the northern base of the Adirondacks^, entered 

 and turned what had been a glacial lake into a marine gulf. The 

 changes of the water levels in the Lake Ontario basin, however, 

 have not yet been fully worked out. 



GLACIAL LAKES IN THE BASIN' OF LAKE MICHIGAN. 



LAKE CHICAGO. 



While this complicated history was being enacted in the Huron- 

 Erie-Ontario area the glacial waters in the basin of Lake Micliigan 

 were also undergoing an expansive development. In this case, how- 

 ever, the changes were extremely simple, for until the very last stage 

 no critical ground affording a new outlet was encountered. Such 

 changes as occurred were due to erosion of its outlet or to changes in 

 the volume of discharge. From its beginning as a narrow, crescent- 

 shaped lake at the extreme southern end of the Lake Michigan basin, 

 Lake Chicago expanded northward as the ice receded until two-thirds 

 or thi^ee-fourths of the basin was uncovered, as shown in figures 2, 

 3, 4, and 5. In all probabilit}^ the retreating ice front performed 

 here the same series of oscillations, with strongly marked retreats 

 and readvances, that took place in the Huron-Erie basin. The evi- 

 dence of these oscillations, how^ever, is not generally so well marked, 

 because critical changes were not produced by them. But some of 

 the stronger moraines mark readvances that override beach ridges 

 which had been made just previously. 



The Port Huron moraine skirts the north side of the high gi'ound 

 of the southern peninsula of Michigan and appears to be correlated 

 with the Whitehall moraine of the Michigan basin. 



Studies by Alden, under the direction of Chamberlain, on the west 

 side of the Mchigan basin have developed evidence of a distinct 

 readvance of the ice southward to Milwaukee characterized by a 

 deposit of red till, and this probably correlates with the Whitehall 

 moraine. Later ridges of red till, which come down to the shore of 

 Lake Mchigan near Manitowoc and Two Elvers, Wis., also seem 

 likely to correlate with the Manistee ridges on the east side of the 

 lake. This correlation is inferred not only because of similar posi- 

 tions on opposite sides of the lobe and in reference to earlier 

 moraines, but also because these later morainic ridges do not appear 

 to carry the Glenwood and Calumet (first and second) beaches of 

 Lake Chicago, which are present on the Whitehall moraine. Two 

 lower beaches in the same area seem to have wider connections. 

 The upper one is the Toleston beach, 24 or 25 feet above Lake Mich- 



1 Fairchild and Goldtliwait, personal communication. 



