GEOLOGICAL PAPERS. Ill 



Following the po5t-Glen\vood stage, the water again rose and 



flooded the area above the 610 foot contour. This is marked by 



a hea\y deposit of sand and gravel of an average depth of a foot 



(2-19 inches). It was at this time that the Rose Hill bar was 



formed. It seems evident that if the entire length of this bar 



was formed at the 615 foot level it was constructed largely under 



water as this depth of water (thirt>--five feet) would submerge 



the greater part of the bar from five to fifteen feet. It seems 



more probable that the greater part of this bar south of North 



Evanston was largely formed during the Upper Tolleston stage, 



at which time a beach ridge was formed on the submerged off 



shore barrier, which was doubtless built up to a considerable size 



during the Calumet stage. Resting on the Calumet gravels is a 



large bed of Unios and other mollusks comprising the following 



species : 



Unio crassidens. Quadritla trigotia. 



Unio gibbosiis. Quadrula pustulosa. 



Obliquaria rcflexa. Quadrula undulata. 



Plagiola elegans. Quadrula verrucosa. 



Lampsilis zentricosa. Quadrula lachrymosa. 



Sphcerium stamineum. Quadrula coccinea paupercula. 



Amnicola letsoni. Campeloma integrum. 



Amnicola limosa. Pisidium (several species). 

 Goniobasis liz-escens. 



These mollusks evidently lived during the Upper Tolleston 

 stage when the water had fallen to a depth of twentj- to twentv^- 

 five feet and flooded ever\-thing below the 600 foot contour. At 

 this time the area behind the Rose Hill bar was a large bay seven 

 miles long, from one to 2^ miles in width and from five to 

 twent}- feet in depth, except near the shore, where it doubtless 

 formed an extensive marsh. The beach ridge called the Rose 

 Hill bar was probably built up during this stage, as was also a 

 part of the Graceland barrier and beach, extending from Rose 

 Hill cemeten,- to Lincoln Park. Above the Unios follows a de- 

 posit of silt about a foot in depth which contains the remains of a 

 bird (humerus of a duck) and the bones of several species of fish. 

 This deposit is highly oxidized and probably was a land surface 

 recording the low water stage preceding Lake Algonquin. The 

 presence of fish remains in these deposits clearly indicates the 

 means by which the L'nios were brought to Wilmette Bay from 

 the populated regions south of the Valparaiso moraine. 



Above this stage occur deposits aggregating twenty-two inches 

 in thickness, composed of silt, peat and marl beds, containing such 

 mollusks as 



