450 THE ILLINOIS GLACIAL LOBE. 



determined concerning the development of channels in this region and their 

 modification during- the high lake stage or stages. 



The portion of this beach in Illinois consists mainly of fine gravel, which 

 is usually well worn, but in places has considerable angular material, as if 

 formed rapidly and subjected for but a brief period to the action of the lake 

 waves. The low district along the Chicago River back of this beach has 

 received quite generally a coating of sand several feet in depth, and the 

 -marsh)' tracts in Hyde Park and Lake townships are also covered with 

 sand to a depth of several feet. Excavations have shown, however, that 

 till usually sets in at a depth of 10 to 20 feet or less. (Alden.) 



In Indiana this beach, like the present shore of Lake Michigan, is very 

 sandy. Its dunes, however, seldom reach a greater height than 50 feet, or 

 but one-third to one-quarter the height of dunes on the present shore. 

 Wells along it have occasionally encountered a bed of gravel at the base of 

 the sand at levels corresponding" with the gravelly beaches of the Illinois 

 portion. 



One of the best exposures of this beach is found at the border of the 

 campus of the Northwestern University, at Evanston, Illinois. The follow- 

 ing sections, one taken by Dr. Oliver Marcy, in 1864, at which time there 

 was a peculiarly good exposure, the other taken by the writer in 1887, at 

 which time there was a less extensive exposure, show a slightly different 

 section. The beach in this interval had suffered an erosion of perhaps 75 

 or 100 feet. 



Section of beach at Evanston made in 1864. 



Feet. 



Surface soil, sandy 1| 



Brown sand and fine gravel 2A 



Coarser gravel, stratified 2i 



Fine sand 2 



Gravel, containing bones of deer .- li 



Fine sand, containing oak logs 1+ 



Peat or carbonaceous eartb with a marl bed containing molluscan shells in the lower portion, or 



interstratified with the peat U 



Gravel 3± 



Hnnius soil, with stumps and logs (coniferous) £ 



Yellow clay, laminated and contorted, containing pockets of gravel 3+ 



Blue, pebbly clay , 2 



Height of bluff 22 



