CHAPTER III. 



RED CLAY AND DRIFT OF GREEN BAY AND WISCONSIN. 



One of the most striking geological features of the region of the great North 

 American lakes is the universal presence of loose diluvial matter, deposited since 

 the convulsions that have taken place in the metamorphic and igneous rocks. 

 Although the general elevation of the superficial materials is not very different, 

 each lake seems to have a system of its own, differing in colour and stratification 

 from the rest. On Lake Champlain and the valley of the St. Lawrence, to a 

 height of five hundred feet above the ocean, marine shells are found in the drift. 

 On Lake Erie, the beds of marly clay and sand which surround its western half, 

 elevated from five hundred to six hundred and fifty feet above tide-water, are 

 almost destitute of shells ; and those rare ones yet found are fresh-water and land 

 shells. These are a Planorbis and a Helicina, found by myself in the " blue marly 

 clay" stratum at Cleveland, fifteen feet above the lake-level, the same I had seen 

 in the Loess of New Harmony and St. Louis. 



The Lake Erie System extends across Canada and Michigan, by way of Lake St. 

 Clair and the River St. Clair, to Lake Huron, and embraces a portion of its southern 

 extremity. 



Rising from Lake Michigan there is another deposit, covering a large tract in 

 Wisconsin, of a very different external cast. This is the " red clay" deposit, which 

 is seen at Milwaukie on the south, and traced by me without interruption to the 

 Falls of Wolf River. At Sheboygan, it extends more inland than at Milwaukie, 

 and is seen to the foot of the high gravel ridges dividing the waters of Sheboygan 

 River from those of Rock River and Lake Winnebago. After crossing this ridge, 

 it reappears in the valley of Lake Winnebago, at an elevation of one hundred and 

 fifty to two hundred and fifty feet above its surface, equal to four hundred and ten 

 feet above Lake Michigan, or nine hundred and eighty-five above the ocean. The 

 valleys of Lake Winnebago, and the Fox (or Neenah) and Wolf Rivers, and the 

 peninsula between Lake Michigan and Green Bay, are composed of this clay ; and 

 it is so uniform in its composition and colour, that specimens taken from Lake 

 Shawano, and Lake Winnebago, from Green Bay or Milwaukie, could not be identified 

 if the labels were misplaced. Tt is so argillaceous, that bricks are everywhere made 



