1905] T RAN SEAU BOGS OF THE HURON RIVER VALLEY 355 



to the Kankakee River, and reached the Mississippi by way of the 

 Illinois. 



As the reentrant extended itself further to the northeast, another 

 channel was opened for the Huron drainage westward past Pinckney 

 into the Grand River, and from there to Battle Creek and the Kala- 

 mazoo River. Below the city of Kalamazoo it cut across to the Paw 

 Paw River, and reached the Mississippi by way of Lake Chicago. 



When the ice of the Erie lobe had retreated as far eastward as 

 Ann Arbor, and all of the interlobate moraine had been uncovered, 

 a third outlet for the waters of the Huron was opened by way of 

 Clinton and the Raisin River, which at that time emptied into glacial 

 Lake Maumee at Adrian (32, pi. 20). This lake was drained by 

 the Wabash River into the Mississippi. 



As soon as the ice margin passed the clay morainic belt already 

 described, the Huron reached Lake Maumee at Ypsilanti by way of 

 its present channel. But Lake Maumee had meanwhile changed 

 its outlet to the northward, its drainage going by way of Imlay (53) 

 to the Grand River, Lake Chicago, and the Mississippi (32, pis. 

 21, 23, 26). 



Later the Erie basin was entirely freed of ice, and its water for 

 the first time flowed eastward into the Ontario basin (glacial Lake 

 Iroquois), and thence by way of the Mohawk to the Hudson. With 

 the clearing of the St. Lawrence channel the present system was 

 inaugurated. 



Aside from the physiographic interest connected with their early 

 history, these glacial drainage channels are of distinct biological 

 interest. They furnish continuous lowland habitats extending in 

 all directions. In so far as they are represented by broad, open 

 valleys, and connect with tributaries of the northern Ohio valley, 

 they provide important highways for the dispersal of southern river- 

 valley species. 



FORESTS. 



The three topographic divisions already described exhibit marked 

 differences in their forest aspect. On the lake plain we find the 

 richest and most mesophytic of the forest types. This lowland 

 habitat is a continuation of the northern Wabash valley, and it is not 

 surprising that its flora should be of much the same character. Here 



