374 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



appearance of a glacial gravel plain. Tributary plains enter near this vil- 

 lage from the Scioto moraine on the east, and the valley soon becomes 

 broader, having in Champaign County a width of 2 to 3 miles. The pres- 

 ent stream has cut but a shallow channel in the upper half of its course 

 and in flood seasons still ovei-flows the bed of the glacial stream, though 

 it has here, as throughout its entire course, an average fall of about 9 

 feet per mile. The moraine comes down to the border of this plain west 

 of West Liberty, and probably glacial waters issued from it at this point 

 into the Mad River Valley. 



About 6 miles below West Liberty a gravel plain enters the valle)'- 

 from the northwest. It is nearly a mile in average width, and extends fully 

 3 miles back into the moraine. At its northwest end this tributary gravel 

 plain grades into and fits about the morainic knolls, showing that it is of the 

 same age as the moraine. The plain is traversed by two streams. Muddy 

 and Crayon creeks, whose beds are only 12 to 15 feet below the level of 

 the plain. Orie of these streams enters from the north and the other from 

 the southwest side of the gravel plain, and they take parallel courses 

 through it, being distant from each other one-half mile or more. The 

 size of their valleys compared with that of the plain which the}' enter is 

 an indication of the small amount of work they have accomplished com- 

 pared with that accomplished by the glacial stream which formed the 

 gravel plain. 



A few miles ftirther south, and nearly opposite Urbana, another tribu- 

 tary glacial gravel plain enters Mad River Valley from the west. This 

 plain is 80 to 160 rods in width, and is traversed by Nettle Creek, the 

 source of the stream being near the head of the gravel plain. It lies in a 

 valle}" which is continued farther west, and into which the moraine descends 

 at the liead of the gravel plain, there forming the divide between Mosquito 

 Creek, a tributary of the Great Miami, and Nettle Creek, a tributary of 

 Mad River. The peculiar features here produced by the ice sheet merit a 

 brief description. The moraine consists of a series of gravelly humnaocks, 

 rising on!}-' 10 to 20 feet above the level of the head of the gravel jjlain, 

 which occupy the valley for less than one half mile, and into which the 

 gravel plain merges as if it had been formed in comiection with them. The 

 same knolls stand about 60 feet above the level of Mosquito Lake, a lake 

 which forms the head of Mosquito Creek, the stream leading northwest 



