413 



tributary. It shows the filled-in material to be eighty-eight feet deep ; 

 that makes the old tributary somewhat below the present level of Raccoon 

 Creek, where the present tributary enters. But not more than thirty rods 

 to the northeast of the well, limestone outcrops. This indicates that the 

 long hill protruding westward from section 24 was continued as the north- 

 ern divide of the old tributary. 



THE PRE-GLACIAL GEOLOGY OF FLATWOODS. 



In considering the geology of the Flatwoods region, it is thought best 

 to divide it into two main divisions. The first division includes the rock 

 structure of the region and the subsequent history up to the Pleistocene. 

 The second division begins with the Pleistocene and takes in all up to the 

 present. The rock structure of the region and immediate vicinity is of 

 Middle Mississippian age with some Pennsylvanian bordering closely on the 

 west. The stratigraphy of the region will be given a brief treatment. 



Knobstone Group . Just to the east of the region in the valley of 

 Jacks Defeat Creek, are the upper portions of the thick Knobstone Group 

 of shales and sandstones. The area of its outcrop in Indiana is a strip of 

 territory some twenty-five miles wide, extending north, northwest from 

 Floyd County to Benton Countyy. This formation consists of compact, insol- 

 uble, impervious sandstones and shales, aggregating a thickness from 400 

 to 600 feet. The topography of the outcrop, resulting from the peculiar 

 weathering of the rocks, is of a distinct type. The rocks absorb water 

 readily, but transmit it poorly, so that they are easily shattered by freezing 

 and thawing. The region is weathered and eroded into deep, steep-sided 

 valleys of very pronounced relief. Brown County affords a typical example 

 of Knobstone topography. Another characteristic of this group of rocks is 

 the general absence of fossils, such being present only very locally. It 

 seems that the shales and sandstones were laid down in impure, muddy 

 waters, which were not on the whole very favorable for the life of water- 

 breathing animals. 



Horrodsburg Limestones. Overlying the Knobstone is the Harrodsburg 

 limestone, with a thickness varying from sixty to 100 feet. This limestone 

 consists of several heavy bedded layers of hard, gray to blue, often highly 

 crystalline stone. There are occasional intercalated thin beds of shale. 

 In some sections a very cherty layer occurs. The top member of this 

 stone often is very massive, and its texture is very similar to the oolitic 

 bed overlying. Geodes are characteristic. The limestone as a whole is 



