THE GLACIAL LAKE CHICAGO. 445 



All excellent exposure of the structure of the bar noted above is found 

 immediately north of Evanston, where the lake is undermining the bar as 

 well as subjacent deposits. The gravel and sand forming the bar rest upon 

 a bed of peat, which was long since noted by Dr. Edmund Andrews and 

 interpreted by him to be the accumulation of a marsh or partially sub- 

 merged land surface. 1 The peat not only underlies this bar, but extends 

 eastward across the interval between it and the Third beach. Its level is 

 no higher than that of the Third beach, being only 12 to 15 feet above the 

 present level of Lake Michigan. The peat is in places several feet thick, 

 but at the point where the bar comes out to the lake shore it has a thick- 

 ness of only a few inches. It there contains pieces of wood which show 

 evidence of disturbance by waves. Between the peat and the yellowish 

 blue till that forms the base of the exposure there is a gravelly sand 6 to 

 18 inches in thickness which appears to be a lacustrine deposit. The peat 

 is immediately overlaid by about 5 feet of sand, above which there is a bed 

 of coarse gravel. The gravel is thin near the borders of the bar, but has a 

 thickness of 10 or 12 feet at the highest part. It is capped by a thin deposit 

 of sand, and has also layers of sand interbedded in its thickest part. The 

 presence of this gravel makes it certain that the old marshy land surface 

 has not been buried by the drifting of material from the lower beach. 

 There seems no escape from the conclusion that the lake stood at a lower 

 stage than the level of the Second beach before that beach and the bar 

 under discussion were formed. 



For a few miles in the vicinity of the State line of Indiana and Michigan 

 there are exposures of peaty material along the bluff of Lake Michigan at 

 levels ranging from about 15 feet above the lake down to the water's edge. 

 The peaty layers are seldom more than 6 inches thick and are interbedded 

 with sand. One layer standing 12 to 15 feet above the lake appears 1^ to 

 2 miles southwest of New Buffalo and is traceable continuously for fully 

 one-half mile. Near Michigan City peaty layers just above the water's edge 

 are nearly continuous for a distance of a mile or more, and occur at frequent 

 intervals from Michigan City to the Michigan State line. Above the peaty 

 beds pebbly sand in places reaches an elevation of 30 feet above the lake, 

 or nearly to the level of the Second beach. The peat appears, therefore, to 



1 Trans. Chicago Acad. Sci., Vol. II, 1870. 



