THE SHELBYVILLB MORAINE. 209 



material is very coarse at this point compared with that above or below, 

 there being many bowlders, as well as cobblestones, embedded in the 

 gravel. Were there no basins, the coarse material found in this portion of 

 the terrace might be explained as a product of subsequent streams working 

 upon the portion of the Shelbyville moraine which had been laid down 

 within the valley, but the basins favor the view that this portion of the 

 terrace is the product of the headwaters of a glacial stream. The removal 

 of fine material from this terrace seems to indicate that there was good 

 drainage at the time it was forming, a view which does not readily har- 

 monize with the silt deposition along the valley. 



Passing west to the Embarras Valley, which leaves the Shelbyville 

 drift near the line of Coles and Cumberland counties, one finds evidence of 

 a moderate discharge of water down the valley. The outer face of the 

 moraine contains knolls of gravelly constitution in the immediate vicinity 

 of the Embarras River, and among these knolls there are plane-surfaced 

 tracts of gravelly material having the appearance of being the deposit of 

 streams issuing from the ice margin. On the immediate borders of the 

 Embarras Valley there is still better evidence of glacial outwash. Gravel 

 deposits form a sheet which caps the till to a depth of several feet and which 

 declines rapidly from the crest of the main ridge southward to the plain 

 outside the moraine, occupying a very shallow valley in the passage down 

 the slope of the moraine. Remnants of this gravel, preserved along the 

 brow of the bluffs, stand 90 feet above river level at the northernmost point 

 noted (2 miles north of the county line), and but 70 feet opposite the ford 

 at the county line, and 45 feet at the south edge of the moraine about 2 

 miles farther south, and 35 feet above the river at the oxbow curve a mile 

 farther south. The rate of descent is, therefore, about 10 feet to the mile 

 more rapid than that of the present stream. At the north the gravel over- 

 wash stands 35 feet above the level of the base of the Shelbyville drift 

 sheet, whose limits are here well defined by a white clay such as caps the 

 older drift outside the Shelbyville sheet. At the south border of the Shel- 

 byville drift the surface of the gravel stands 25 feet below the level of the 

 white clay; it therefore cuts right down across the plane of the white clay. 

 The valley of the Embarras above the south edge of the Shelbyville sheet 

 has probably been excavated entirely since the Shelbyville drift was 



MON XXXVIII 14 



