343 | 
THE PREGLACIAL DRAINAGE OF THE BASIN OF THE WABASH 
AND LOWER OHIO. 
About one-half of the drainage basin of the Wabash river is so deeply 
buried under glacial deposits that there is very little similarity between the 
modern watershed and the watershed of the preglacial streams that dis- 
charged through the lower course of the Wabash. The preglacial rock sur- 
face was probably very rough, for the drift varies within short distances 
from a few feet to over 200 feet in depth. 
The Wabash river at Lafayette is flowing in its original channel. 
Below Lafayette the preglacial channel runs westward and then southward, 
meeting the present Wabash at Covington. Below Covington the present 
river follows the ancient channel. Nothing is known of the upper portion 
of the preglacial Wabash above Lafayette. A study of the drift covered 
rocks reveals a divide extending south along the west side of Lake Mich- 
igan, and curving to the east into Indiana. It is from 100 to 200 feet above 
Lake Michigan and is deeply sculptured by preglacial streams and thor- 
oughly drift covered. It has been suggested that the Lake Michigan basin 
was the headwater portion of the Wabash in preglacial time. On this point 
Leverett says (62): “The headwater portion of the Wabash stream form- 
ing the preglacial Wabash may prove to have been in the Lake Michigan 
basin. But if so the connection with the Wabash is through a very much 
narrower trough than that occupied by Lake Michigan. Borings at both 
North Judson [497 ft.], Winamac [490 ft.] and Monticello [467 ft.], Indiana, 
situated near the line connecting the heads of Lake Michigan with the pre- 
glacial valley at Lafayette, go to a level about 100 feet below the surface of 
Lake Michigan before entering rock. But within a few miles east of this 
line rock ledges have an altitude as great as the surface of Lake Michigan, 
while immediately west of this line they rise 90-125 feet above that level. 
This trough can not have, in the vicinity of Monticello, a breadth of more 
than ten miles. Monticello is situated near the middle of the trough. The 
probabilities are, therefore, against the existence of a much deeper channel 
LE Whe 
Leverett (65) suggests that the old channel which passes into Grant 
County from Ohio may be a headwater portion of the preglacial Wabash. 
The modern Wabash has not completely excavated the ancient valley to its 
full width above Terre Haute, but below that city the excavation is more 
nearly complete. 
