60 PLEISTOCENE OF INDIANA AND MICHIGAN. - 



another from the east, both joining it not far from the city of Lafayette. The one from the 

 north probably carried the drainage of a considerable part of northern Indiana, and possibly 

 was the line of discharge for the southern portion of the basin now covered by Lake Michigan. 



A preglacial valley, which has been traced from Celina, Ohio, westward into northern Indiana 

 and which passes near Geneva, Hartford, Marion, and Peru, probably belongs to the same 

 system as that draining northern Indiana; in this valley the drift is nearly 400 feet thick, 

 whereas on the interfmvial tracts on either side it is less than 100 feet thick. The presence 

 of such valleys must be taken into account in estimating the thickness of' drift. 



In the southern peninsula of Michigan one of the most important preglacial valleys leads 

 from the head of Saginaw Bay southwestward into Gratiot County and thence westward and 

 northwestward to the Lake Michigan basin north of Ludington. (See PI. IV.) It indicates a 

 drainage from the Saginaw basin to the basin of Lake Michigan, as the floor becomes lower in 

 passing westward from Saginaw Bay. 



PRESENT-DAY DRAINAGE SYSTEMS. 



Tire greater part of Indiana is tributary to the Wabash, itself a tributary to the Ohio; 

 the southern end of the State is directly tributary to the Ohio through smaller streams; the 

 northeastern part drains through the Maumee to Lake Erie and the northwestern part largely 

 through the Kankakee to the Illinois, though a narrow strip drains to Lake Michigan. The 

 southern peninsula of Michigan drains entirely to the Great Lakes, the western half to Lake 

 Michigan, and the eastern hah chiefly to Lake Huron and its arm, Saginaw Bay, though some 

 small areas in the southeastern part drain to Lakes St. Clair and Erie and to St. Clair and Detroit 

 rivers. 



The boundaries between the several river systems fall mainly within the glaciated region 

 and are largely determined by glacial accumulations. The only important water partings 

 within the glaciated portion of Indiana which to any marked degree coincide with the elevated 

 rock surfaces are in southern Randolph County between the headwaters of White River, a 

 tributary of the Wabash, and those of Whitewater River, a direct tributary of the Ohio; but 

 even here the water partings result only in a general way from the elevated rock surface, their 

 precise position being determined by morainic accumulations. The water parting between 

 the tributaries of the Wabash and the small tributaries of the Ohio in southern Indiana from 

 the meridian of Salem westward is chiefly due to rock irregularities, for most of the small Ohio 

 tributaries he wholly in unglaciated territory; but from near Salem eastward the water parting 

 is inside the glacial boundary and is only in a general way dependent on the rock surface. 



In the southern half of Michigan the high altitude of the rock surface determines in a 

 general way the divide between the westward drainage to Lake Michigan and Saginaw River 

 and the eastward drainage to Lake Huron, St. Clair River, Lake St. Clair, Detroit River, and 

 Lake Erie. In the remainder of the southern peninsula the water partings show little or no 

 dependence on the rock surface. 



DEVELOPMENT OF PRESENT DRAINAGE. 



Some of the present drainage did not come into existence directly on the withdrawal of 

 the ice. During the occupancy of the immediate basins of Lakes Michigan, Huron, and Erie 

 by the ice sheet the territory to the south was tributary to Mississippi River either through 

 the Wabash and Ohio, the Kankakee and Illinois, or the Desplaines and Illinois. Lakes 

 held between the ice and the present St. Lawrence-Mississippi divide discharged across the 

 latter through large and well-defined outlets, that to the Wabash being known as the Fort 

 Wayne or the Erie-Wabash outlet and that to the Desplaines as the Chicago outlet. Glacial 

 lakes discharged also through outlets leading across the southern peninsula of Michigan, con- 

 spicuous among which were the Imlay, the Ubly, and the Grand River outlet. 



Little of the present drainage within the glaciated portion of this region coincides for any 

 great distance with the preglacial lines. Many of the streams are too shallow to reach the 



