THE CLYDE SERIES OF SOILS. 7 



was increased, covering what is now the southern end of Lake Michi- 

 gan. In consequence, only small areas of glacial lake material now 

 form the land surface around the southern extremity of that lake. 

 In the case of Lake Maumee the gradual recession of the ice gave 

 rise to the formation of glacial lake materials covering an area 

 of more than 4,000 square miles in northwestern Ohio, northeastern 

 Indiana, and southeastern Michigan. In fact, the entire Maumee 

 Basin and the adjacent territory, extending from the vicinity of 

 Fort Wayne, Ind., past Sandusky, Ohio, on the south and to the 

 vicinity of Port Huron, Mich., on the north, was occupied by a suc- 

 cession of glacial lakes whose characteristic topography and dis- 

 tinctive soils now constitute the principal surface features of that 

 region. 



At the same time a considerable area of low-lying land to the 

 south and west of Saginaw Bay, in Michigan, was occupied by glacial 

 lake waters at several successive periods. It is probable that the 

 total area formerly occupied by glacial lake waters around Saginaw 

 Bay amounts to approximately 2,500 square miles. 



A similar area was occupied by glacial lake waters standing at the 

 lower levels around the head of Green Bay, in Wisconsin, and south- 

 west past Fond du Lac. The total area of glacial lake sediments in 

 the latter region is possibly as great as 1,000 square miles. 



During these earlier stages of ice recession and glacial lake occu- 

 pation the outlets for the ponded waters were through the Des Plaines 

 River into the Illinois River, for Lake Chicago; past Fort Wayne 

 into the Wabash River, for the first Lake Maumee; and around the 

 " thumb " of Michigan through Lake Saginaw and thence down the 

 Grand River to Lake Chicago for the more northern waters. As the 

 ice still farther receded, a passage for the impounded water was un- 

 covered to the eastward between the ice front and the higher lying 

 plateau country of northwestern Pennsylvania and western New 

 York. For a time, at least, an outlet was established through the 

 Mohawk Valley, while at a later stage the drainage way through 

 the St. Lawrence River was uncovered. Still later, marine waters 

 occupied the St. Lawrence Valley and a small area around the outlet 

 of Lake Ontario. Thus a series of glacial lakes was formed along 

 the southern shores of Lakes Erie and Ontario and within the St. 

 Lawrence Valley. 



FORMATION OF GLACIAL LAKE DEPOSITS. 



During all of these successive stages of glacial lake occupation, 

 distinctive lake sediments were deposited at the different levels, de- 

 scending from an altitude of about 800 feet for the higher stages of 

 the more western lakes to the present level of the upper Great Lakes. 

 In the more eastern areas south of Lake Ontario the elevated plateau 





