438 THE ILLINOIS GLACIAL LOBE. 



a higher level than that of the upper beach at the point where it comes to 

 the lake in northern Cook County, the altitude being about 90 feet above 

 the lake. But observations by the writer in northern Lake County, Illinois, 

 and by Professor Charaberlin in southeastern Wisconsin indicate that the 

 upper beach continues at about 50 or 60 feet above Lake Michigan. 



A few gravel pits have been opened in the upper beach in the vicinity 

 of Chicago. Probably the most extensive is Haas's pit, near Forest Home 

 Cemetery, 1 mile south of Oak Park. This is opened in the bar described 

 above as leading southward on the east side of the Des Plaines River. 

 The excavation extends from the east side of the bar west past the center, 

 and shows beds dipping at various angles, but all toward the east. The 

 lower bed, which is mainly sand, decreases in thickness in passing from the 

 higher to the lower part of the bar. The overlying beds are thin on the 

 higher part and increase in thickness toward the east border of the bar. 

 The coarser deposits appear to be built upon the sand bar, as may be seen 

 l>v the following section. Mr. Haas states that the material of the same 

 bed may vary greatly in coarseness within the space of a few feet, but that 

 throughout the entire extent of the pit, which covers an area of several 

 acres, the dip of the beds is uniformly toward the east: 



Section in Haas's gravel pit, near Oak Parle, Illinois. 



Inches. 



Brown stained gravel capping summit and slope 18-30 



Fine gravel, fresh or stained but little 24-48 



Sand, very thin at top, but increasing toward side of ridge 0-36 



Fine gravel, increasing toward side of ridge 0-48 



Fine gravel, which passes upward from near the east side of the excavation, assuming a nearly 



horizontal position beneath the crest of the ridge 40-48 



Sand, thickening toward the higher part of the ridge 6-36 



Another gravel pit has been opened in the beach between Salt Creek 

 and Lagrange, in which the excavation extends from the east side of the 

 beach westward nearly to the outer slope. It has a depth of 12 to 14 feet, 

 and exposes a series of beds dipping slightly toward the east. The upper 

 5 feet is of brown stained gravel; the lower portion is a fine gravel with 

 very little stain. In the gravel there are sandy pockets and also thin beds 

 of sand. These sandy portions in some cases show a slight effervescence 

 with acid, but are not nearly so calcareous as sand found at similar depth 

 in glacial deposits. 



