238 G. F. WRIGHT ABANDONED BEACHES ABOUT LAKE MICHIGAN 



It is difficult to see the force of this suggestion of Mr. Leverett. How 

 could a thickness of 10 or 13 feet of gravel, capped hy a thin deposit of 

 sand, be pushed out into water of considerable depth to cover a deposit 

 of peat that was originally at the level of the southward moving currents 

 which deposited the bar? The conception is impossible. We shall be 

 justified, therefore, in accepting the original conclusions of Doctor 

 Andrews and Mr. Leverett, which were formed when these Evanston de- 

 posits were all exposed. Unfortunately, at the present time the growth 

 of the city has so modified the sliore that the facts are not now^ open to 

 inspection. 



Speaking further of the peat deposits near ]\Iichigan Cit}', he says : 



"The sand evidently was deposited during the development of that beach 

 nnd the peat is certainly as old as the beach. The beach may have been ex- 

 tended out over a peaty deposit, as w^as suggested in the case of the Evanston 

 deposits, but the conditions on the whole do not strongly favor this view." •' 



To establish the early date of the peat, Mr. Leverett would demand the 

 discovery of valleys which entered the lake at this lower stage, at a level 

 below the Calumet beach, and which had been built across by the Calumet 

 beach ; but in the lack of such evidence it is not necessary to give it much 

 weight. 



The Seeies of Moraines 



As will be seen from the map, the outlet has two branches coming to- 

 gether at the Sag. These are separated by Mount Forest Island, which 

 is in the main a moraine deposit. From the Sag westward through 

 Lemont to Lockport the channel is on a dead level, running over a rock 

 shelf 8 feet above Lake Michigan. At Lockport it descends through 

 Joliet and some distance below, 35 or 10 feet in a few miles. At the 

 foot of this descent there are immense gravel deposits (including many 

 boulders a foot or more in diameter) on the west side of the Des Plaines 

 River, rising 60 feet above the river plane and covering fully a square 

 mile. The gravel is also 40 feet in depth below the river plane. 



Properly to interpret the histor}^ of this outlet, we must consider the 

 series of moraines on the west side of the lake. The outer moraine is 

 many miles in width, extending all around tlie south end. It is called by 

 Leverett the Valparaiso moraine. North of the outlet there are two or 

 three narrow parallel moraines extending from the north, but at present 

 not reaching the south end of the lake. Numbering from the west, the 

 Clalewood moraine is se])arated from the Valparaiso moraine by a valley 

 2 or 3 miles wide, throuoh which the Des Plaines Elver flows. A little 



Ibid., p. 856. 



