100 THE ILLINOIS GLACIAL LOBE. 



The present Patoka Kiver leads southward from Jasper for several 

 miles, occupying - the northern end of the broad valley of Hunleys Creek, 

 a southern tributary of the abandoned valley just discussed. The river then 

 takes a northwestward course, cutting across a narrow neck of upland and 

 touching the border of the abandoned valley about 2 miles south of Ireland. 

 In this passage across the neck of upland the width of the flood plain is 

 nowhere less than one-fourth of a mile, or about double the width of the 

 valley bottom in the gorge at Jasper. Whether this difference in size is 

 referable to variations in the texture of the rock or is due to difference in 

 date of deflection has not been determined. It seems, however, not improb- 

 able that this narrow neck had been encroached upon t by valleys on each 

 side and severed from the main upland prior to the glacial invasion. 



After touching the old valley near Ireland, the Patoka turns to the 

 southwest and near the line of Dubois and Pike counties enters a narrow 

 valley 800 to 1,000 feet in width. The narrow portion extends from the 

 county line southwest about 2 miles to the mouth of Rocky Creek, a south- 

 ern tributary. It there expands to twice or three times the width of the 

 narrow portion and from that point gradually increases in width down the 

 stream, reaching nearly 2 miles in western Pike County. The narrow por- 

 tion evidently marks the position of a preglacial divide. That this divide 

 had been reduced to a low elevation is shown by neighboring cols, which, 

 though low, were not utilized by this stream in selecting- a new course. One 

 of these cols at the village of Velpen stands only 510 feet above tide. It 

 is probable that the blockaded stream had to rise no higher than 500 feet to 

 cross the divide, or to a height of less than 75 feet above its present level; 

 possibly the divide was not more than 475 feet at the col. The latter alti- 

 tude is slightly lower than the sand and silt filling made by Lake Patoka 

 which, as above noted, is found in the abandoned valleys to the north and 

 east of this divide. This filling is conspicuous in the vicinity of the divide 

 as well as above, and seems to pass down the present stream beyond the 

 divide without appreciable decrease in altitude. The col was nearly if not 

 quite covered by silt before the present channel was opened across it. 



The Patoka River apparently follows the line of a preglacial stream 

 from the mouth of Rocky Creek, in eastern Pike County, westward into 

 Gibson County to the bend about 6 miles above Patoka, It there is in a 

 low tract which extends northward to White River. But instead of follow- 



