STRUCTURE OF THE DRIFT BORDER. 69 



uplands to the south it is found at 6 to 10 feet, there being little, if any, 

 drift present. 



As already noted, in northwestern Dubois County there is a low plain 

 covering about 50 square miles in which the loess is underlain by sand. 

 The sand appears to have been deposited in the glacial lake Patoka, formed 

 by the obstruction of the Patoka River by the ice sheet, the preglacial 

 course of the river having been northwestward across this plain into East 

 White River. The plain was built up to a level of about 480 feet above 

 tide, which has been increased to 485 to 490 feet by the subsequent loess 

 deposit. The surface of the sand at the base of the loess is deeply weather- 

 stained, showing that it long antedated the loess in deposition. On the 

 borders of this plain, about 3 miles north of Jasper, in sec. 15, T. 1 S., 

 R. 5 W., an exposure of black soil was found immediately below the loess, 

 which was apparently formed in the Sangamon interglacial stage. The 

 clay below it contains a few glacial pebbles. 



In southeastern Daviess County, as noted above, the drift for a mile or 

 two back from the glacial boundary is reduced to a few scattering pebbles. 

 A heavy sheet of till there sets in, which fills the country to a nearly 

 uniform level and produces plains known as "the flats," on which the drift 

 ranges from 20 to 80 feet or more in depth. The plane surface extends 

 nearly to the glacial boundary in the vicinity of Whitfield, Mount Pleasant, 

 and Loogootee, in Martin County. There are, however, scattering pebbles 

 on the hills along the east border of the plain. On a tributary of Boggs 

 Creek, 2 miles north of Loogootee, exposures of till occur 30 feet or more 

 in height, in one of which a granite bowlder 4 feet in diameter was noted. 

 Along much of the boundary from Loogootee to Scotland the drift is very 

 thin, though it apparently forms a nearly continuous sheet. There are low 

 hills along the east border of Daviess County which for several miles inside 

 the g'lacial boundary show only a thin coating of drift. But the lowlands 

 in that region have apparently been filled to considerable depth. 



At Scotland and along ravines northeastward there are exposures of 

 sandy till 10 to 20 feet in depth at points within a mile of the apparent limits 

 of glaciation. The hills in that region, however, carry very little drift. 



In the lowland tract north of Plummer's Creek there are heavy depos- 

 its of sand, which in places are capped by a few feet of fine gravel, apparently 

 a glacial deposit. The filling amounts to 75 or 100 feet, and seems excess- 



