WABASH RIVEK DRAINAGE BASIN. 529 



discharge through the lower course of the Wabash. The westward-flowing 

 portion of the Wabash, with its several tributaries, traverses- a district tying 

 mainly outside the limits of the Illinois lobe and appears to be entirely 

 independent of preglacial drainage lines, for the drift deposits have been 

 built up to a level above the preglacial rock divides. The headwater por- 

 tions of White and East White rivers, which are the principal tributaries of 

 the Wabash, seem also to be very largely independent of preglacial lines. 

 There remain only the lower courses of the Wabash, and of tributaries 

 entering below the great bend near Covington, Indiana, which are governed 

 to any considerable extent by the preglacial lines of drainage. These all 

 fall within the limits of the Illinois lobe or of unglaciated districts immedi- 

 ately outside. 



Only the tributaries of the Wabash which enter within the limits of 

 the Illinois glacial lobe are discussed in this place. The remainder of the 

 watershed falls within the limits of a district covered by another report, 

 now in preparation. 



THE PREGLACIAL WABASH VALLEY. 



. The Wabash River enters a preglacial valley just above the city of 

 Lafayette, which probably furnished a line of discharge for a considerable 

 territory on the north and west. The river, however, remains in this 

 preglacial valley for only a few miles; it soons turns south westward across 

 a rock point, while the preglacial valley apparently takes a longer route to 

 the west and south, coming to the river at its great bend near Covington. 

 From Covington southward the stream follows nearly the line of a preglacial 

 valley to its mouth, though in a few places it cuts off rock points which 

 ■ projected into the preglacial valley. 



Above Terre Haute this preg'lacial valley has been opened only a part 

 of its width by the present stream, yet it shows a breadth of 2 to 4 miles. 

 Below Terre Haute the bottoms of the present stream extend from bluff to 

 bluff of the preglacial valley. The breadth increases from about 5 miles at 

 Terre Haute to fully 15 miles near the junction of the Wabash with the 

 Ohio. 



Few data have been obtained concerning the elevation of the rock 

 bottom, but these uniformly indicate a level considerably below that of the 

 present stream. So far as collected, they do not show a descent in passing 



MON XXXVIII 34 



