] 88 Wisconsm Academy of Sciences^ A^is and Letters. 



in height, capped by a slight deposit of beach gravels. Its elevation is but, 

 13 feet above Lake Michigan, for two miles or more from Lake Calumet, 

 but further west it is 15 — 30 feet. Low as it is, it marks a quite distinct 

 change in the surface deposit. On its east side is a sand deposit, 1-18 feet 

 in depth, but on the west there is a pebbly clay, except along beach lines 

 already described. 



A second beach hes about a mile west from the one just described. It is a 

 bench or low sea cliff 10-13 feet in height along its southern part, but less 

 in the northern part. It can be traced easily from the Calumet river, near 

 Riverdale, north through Kensington, to the northwest corner of Sec. 15,^ 

 Tp. 37 N. , R. XIV W. , where it merges into the plain which borders it„ 

 South of the Calumet river, in Riverdale, is a ridge of sand and gravel 

 which is probably of the same age as the bench at Kensington. It has a 

 course almost due southeast to the Indiana line, entering that state about 

 1+ miles south of Hammond. 



An interesting problem arises as to the outlet of Lake Michigan at the 

 time the lower beach was forming. There may have been a narrow outlet 

 through the Calumet, from Riverdale to Blue Island, and thence through 

 " the sag," into the Des Plaines valley. There may have been another from 

 near Lake Calumet, just between the Englewood beach and the low benches 

 above described, into the Chicago river near the Union Stock Yards, and 

 thence west through a marshy tract called " Mud Lake," to the Des Plaines 

 river. There may also have been an outlet via the Chicago river, through 

 the city to " Mud Lake," and thence into the Des Plaines valley. There are 

 no points along any of these low belts that exceed 16 feet above the present 

 level of the lake, and those via. " Mud Lake " are in no case above 10 feet. 

 Probably the whole region in and near Chicago, whose elevation is 15 feet 

 or less above Lake Michigan, ^vas covered with ^vater at the time when 

 this beach was forming. It is also probable that the outlet at the north end 

 of Lake Michigan was opened during the period when the lower beach was 

 forming, if it had not opened previous to that time. . . 



We are indebted to Prof. Oliver Marcy, of Evanston, for a careful section 

 of the beach at the lakeshore in Evanston, made in 1864, at which time 

 there was a peculiarly good exposure. The section was exposed north of 

 Heck Hall, at the border of the University campus: 



1. Surface soil, sandy 1}^ feet 



2. Brown sand and fine gravel 2}4 feet 



3. Coarser gravel, stratified 2-^ feet 



4. Fine sand 2 feet 



5. Gravel containing bones of deer 1^ feet 



6. Fine sand containing oak logs 1^4 feet 



7. Peat or carbanaceous earth, with a marl bed containing molluscan shells 



in the lower portion, or interstratifled with the peat 1 J^ feet 



8. Gravel 3J4 feet 



9. Humus soil with cedar stump and logs 4-6 inches 



10. YeUow clay laminated and contorted — containing pockets of gravel 3J/^ feet 



11. Blue pebbly clay 2 feet 



Height of bluff 23 feet 



