WABASH DRAINAGE SYSTEM. 187 



this system being within the hmits of glaciation, and in a region where the 

 drift coating is suflSciently thick to conceal more or less completely the pre- 

 glacial valleys, it has been largely developed in interglacial and ^xost- 

 glacial time. The lower courses of the Wabash, West White, and East 

 White are, however, following nearly the preglacial lines. 



WABASH RIVER. 



The valley occupied by the Wabash River has not had a uniform 

 development from source to mouth. In its upper part, from the source 

 to Huntington, Ind., the valley has been formed chiefly by the present 

 stream, and is a shallow and narrow trench. At Huntington the river enters 

 the old outlet of Lake Maumee, a glacial lake that occupied part of the 

 basin of Lake Erie. This outlet has a valley several times as large as that 

 occupied by the Wabash above this point. It opened a new or postglacial 

 line of drainage in its westwat-d course across Indiana, except for a few 

 miles in the vicinity of Lafayette, where it crosses or follows a preglacial 

 valley for a few miles. It has been compelled to do considerable excava- 

 tion in rock from Huntington down as far as Covington, and still carries 

 rapids at several points. Below Covington the streajn follows very nearly 

 the line of a partially filled preglacial valley, and its work has been largely 

 the removal of a portion of the glacial deposits left in that valley. It 

 makes, however, some deflections into the edge of the uplands, cutting off" 

 points of the bluff's. At such places the channel is occasionally in process 

 of excavating rock. The cause for these deflections is not in all cases clear, 

 but it is probable that in the majoi'ity of cases the filling was such that the 

 stream was free to pass across these points and thus take a more direct 

 course than that of the old line around them. In some cases it is possible 

 that the ice sheet may have had an influence in guiding the stream across 

 projecting points beneath it or on its border. 



The length of the valley occupied by the Wabash is about 450 miles; 

 but the length of the stream is much greater, for the river in its lower 

 course makes several oxbow curves within the valley. The source of the 

 river is about 1,000 feet above tide, while its mouth at low water is but 

 311 feet. The average fall, if we estimate the stream to have a length of 

 500 miles, is therefore about 16 J inches per mile. The rate of descent is 

 far from uniform, being much more rapid in the upper portion than in the 



