PAPERS OX GEOGRAPHY AND GEOLOGY 1S3 



During the existence of these lakes, deposition of ma- 

 terials from the melting ice was constantly going on. In 

 the Craborchard lake, which was probably by far the 

 largest on this quadrangle, it seems possible that un- 

 stratified gray clay accumulated in portions of the lake 

 basin where deposition was continuous. From time to 

 time boulders and pebbles fell from bergs and ice blocks 

 floating about on the lake and became imbedded in this 

 lake bottom clay. Thus it is possible that some of the 

 gray clay till-like material which contains sparse pebbles 

 may have originated. This method of origin does not, 

 however, preclude the probability that the greater part 

 of the gray till was formed in the commonly accepted 

 fashion, but is merely a suggestion as to how a very simi- 

 lar sort of deposit might have been formed under special 

 conditions. 



In the smaller lakes and the larger lake alike there 

 were deposited in considerable thicknesses statified ma- 

 terials composed for the most part of sand and silt. 

 There is some gravel found with these sands and silts. 

 but it occurs in lens-like deposits, some of which seem 

 to have been built up as small deltas where comparative- 

 ly rapid moving water entered a quiet body of water. In 

 some of the smaller valley lakes in the central part of the 

 quadrangle, fifty or more feet of these sands and silts 

 accumulated. They are commonly underlain by pebbly 

 clay till, and in places have this material intercalated 

 with them. The valley of Sycamore Creek, in the east- 

 ern part of T. 10 S., E. 1 W. particularly, has excellent 

 exposures of these sands and silts. 



In two of the lakes the water seems to have become 

 high enough to have spilled across the divide and found 

 an outlet to the south to Ohio Eiver. These lakes oc- 

 curred in the valleys of Drury Creek and Little Gi 



k respectively. The former lake had its inception 

 when the ice shut off the drainage of Drury Creek from 

 Craborchard Creek. By the time the ice had advanced 

 south to a point about a mile and half south of Bosky 

 Dell, the lake was about eight miles long and the water 

 in it at that point was about 2 t deep. The surface 



elevation of the lake was about 600 feet. Some of the 



