112 ILLINOIS ACADEMY OF SCIENCE. 



Lampsilis luteola. Physa ancillaria warreniana. 



SphcErium striatinum. Physa Integra. 



Sphcerimn rhomboideum. Planorbis trivolvis. 



Pisidium (several species). Planorbis campanulatus. 



Campeloma integrum. Planorbis bicarinatus. 



Goniobasis livescens. Lymnaea stagnalis appressa. 



Valvata tricarinata. Galba reflexa. 

 Amnicola limosa. 



The marl deposit is nearly five inches in thickness and is a 

 solid mass of shells. These deposits probably represent the 

 Middle ToUeston stage, which corresponds with the Lake Algon- 

 quin stage of the Great Lakes. At this time Wilmette Bay was 

 three miles long, a mile wide and five to twelve feet in depth 

 behind the Rose Hill bar. It extended, however, five miles south 

 of this bar and was protected from" Lake Michigan by the Grace- 

 land bar, upon which Clark Street is constructed, which rose above 

 the lake nearly ten feet. This bay south of Foster Avenue was 

 five miles long and about one mile wide, with a depth of water of 

 five to twelve feet. The shallowness of the bay is attested by the 

 presence of Potamogeton and Chara, plants which live in com- 

 paratively shallow water. The Middle Tolleston lake bed above 

 the 590 foot contour was an extensive marsh nearly three miles 

 long and over a mile wide, in which the following mollusks lived 

 abundantly : 



Succinea ovalis. Segmentina armigera. 



Succinea avara. Galba caperata. 



Physa gyrina. Galba reilcxa. 



Planorbis trivolvis. Calyculina securis. 



The upper deposit of the Middle Tolleston is oxidized and 

 contains the burrows of crayfish, indicating that this deposit was 

 for a time a land surface. Above this land surface occurs a 

 deposit of peat over five inches in thickness overlaid by twenty- 

 eight inches of silt. This doubtless represents the Nepissing 

 Great Lakes and the Lower Tolleston stage. The water is believed 

 to have been from three to ten feet in depth and the area flooded 

 was probably nearly equal to that of the Middle Tolleston.^ The 

 life of this stage was the same as that of the Middle Tolleston. 

 Following this stage the lake fell to its present level. 



The interpretation of these deposits is not in accord with that of 

 Dr. Goldthwait,'' who places the peat and silt beds found beneath 

 the Rose Hill bar in the period previous to the Upper Tolleston 



BGoldthwait, Bull. 7, 111. Geol. Surv., p. 64; Bull. 11, p. 56, p. 81; Bull. Wi.s. 

 Geol. & Nat. Hist. Surv., XVII, p. 6, 7, et. seq. 



"Bull. Wis. Geol. & Nat. Hist. Surv. XVII, p. 4; also Bulls. 7 and 11, III. 

 Geol. Surv. 



