GEOLOGICAL PAPERS. " 115 



SUMMARY. 

 The study of the strata deposited in post-glacial W'ilmette Bay 

 has led to the following conclusions : 



1. There was but slight deposition during the Glen wood stage 

 and no life. 



2. A post-Glenwood low-water stage ensued in which the 

 level of the lake dropped to about the 590 foot contour, the water 

 being from five to ten feet in depth. There was a rich and abund- 

 ant fauna of mollusks, and the neighboring shore supported a 

 vigorous growth of spruce and oak. 



3. The lake level rose to the 610-620 foot contours (Calumet 

 stage), flooding the silt deposits and burying them under a heavy 

 deposit of sand and gravel. The Rose Hill bar was extended 

 from the shore near Wilmette, southward below North Evanston, 

 as a huge bar, the southern portion forming a submerged reef. 

 No life present. Wilmette Bay was at this stage an open bay 

 from five to thirty feet in depth, protected on the north by the 

 Rose Hill bar and on the east by the submerged reef, rapidly 

 forming. 



4. The water fell to about the 600 foot contour (Upper Tol- 

 LESTON stage), the Rose Hill bar extended southward and was 

 built up on the reef formed during the Calumet stage. The beach 

 ridge, upon which Graceland cemetery is located, was probably 

 formed during this stage, first as a submerged reef, and later as 

 a beach ridge. A rich fauna at this time migrated up the Des 

 Plaines River and formed the heavy Unio beds which are found 

 on the surface of the Calumet gravels. This bay was nearly ten 

 miles long, two to three miles wide and from five to twenty feet 

 deep. 



5. A low water stage followed the Upper Tolleston. This is 

 indicated by the oxidized character of the deposit overlying the 

 Unio bed. 



6. During the next stage, which may be called the Middle 

 Tolleston, the water level again rose to a point somewhat above 

 the 590 foot contour, forming a shallow bay about three miles 

 long, one mile wide and five to twelve feet deep. A rich fauna 

 and flora of swamp and shallow water mollusks and plants devel- 

 oped in this bay, forming deposits aggregating twenty inches in 

 thickness. This stage forms part of Lake Algonquin. 



7. A third low water stage followed the Middle Tolleston. 

 Evidences of this are seen in the oxidized character of the stratum 



