THE LAKE-BORDER MORAINIO SYSTEM. 409 



Plaines also the excavation is largely in drift to the vicinity of Lemont, 

 where the canal becomes a rock channel. From Bridgeport to Summit there 

 is little besides till, but from Summit to Lemont gravel, sand, and the coarser 

 material deposited or left as a residue along the line of the old lake outlet 

 form a large part of the section. 



In the Fullerton avenue conduit, which leads eastward into the lake 

 through the north part of Chicago, the drift is mainly till, but surface sand 

 is a conspicuous deposit. From its western end to within 2,000 feet of the 

 lake the rock surface is found at a depth of 43 to 54 feet. Within 100 feet 

 east from this point it drops down to 80 feet, passes below the conduit, and 

 does not appear farther east. The surface sand has its greatest thickness at 

 about 1,700 feet from the lake, where it reaches 25 feet. It decreases west- 

 ward to only 12 feet at a distance of 6,000 feet from the lake, and entirelv 

 disappears before reaching the Chicago River Valley. Toward the lake 

 shore also it decreases, but holds a thickness of about 18 feet for 1,400 feet 

 from the shore. At the water's edge the depth is but 10 feet. The profile 

 continues out 1,100 feet beneath the lake, and there is but 3 feet of sand at 

 its terminus 



Numerous borings and excavations in the south part of Chicago, in 

 Hyde Park Township, show sand deposits ranging in depth from 5 feet or 

 less up to about 20 feet. Till usually underlies the sand except where the 

 rock comes near the surface. In this connection it maj r be remarked that 

 the heavy deposits of sand in Cook County are found chiefly along the 

 present lake border from Evanston southward, where there is a continuous 

 belt of sand ranging in width from one-half mile to 3 or 4 miles and having 

 an average depth of not less than 10 feet. Over much of the plain west 

 of this sandy belt the deposition was so light as scarcely to conceal the 

 surface bowlders and in places leaves only a trace of sand in the soil. The 

 south-westward lake outlet appears to have carried away much of the sand 

 which was brought into the southern end of the lake while that outlet was 

 open. 



In the portion of Indiana between the Valparaiso morainic system and 

 Lake Michigan sand deposits are heavy as far south as Calumet River in 

 Lake and western Porter counties and nearly as far as the inner border of 

 the till ridge in northeastern Porter and northwestern Laporte counties, a 



