GEOLOGICAL PAPERS 97 



of the highlands. The bluffs rise boldly from eighty to lOO feet 

 above the river flats. They are much dissected by small streams, 

 which have cut through the drift of the Pleistocene, and, wherever 

 the Pennsylvanian is present, through the shales and sandstones 

 of that system, exposing the Devonian limestones below. 



These small streams have comparatively steep gradients and a 

 consequent erosive power of considerable strength. Wherever 

 they cut through the limestones, they have developed rather nar- 

 row valleys with steep banks. The larger of these creeks are 

 Fancy Creek, Case Creek and ]*klill Creek, all affording good 

 exposures of Devonian strata in their banks. 



The drift of the Pleistocene varies much in thickness, in some 

 places scarcely covering the country rock, while on some of the 

 hills, well borings reveal a depth of fifty feet of glacial material, 

 which is probably all of Illinoian age. In the river valleys, mate- 

 rial from the Wisconsin drift to the eastward has been deposited, 

 and in the eastern portion of the area scattered localities of ridged 

 loess and sand occur, which resemble in character those of the 

 lowan drift border. Usually the Pleistocene deposits rest upon 

 those of the Pennsylvanian, but when the latter have been eroded 

 the loess and drift cover the limestones of the Devonian age. 



The Pennsylvanian shales and sandstones of this area, some 

 seventy to lOO feet in thickness, belong to the Potts ville and Car- 

 bondale stages. They overlie the Devonian limestones, which at 

 the time of deposition of the Pennsylvanian rocks formed the well 

 dissected surface of the area. Well defined erosion valleys in 

 the Devonian are filled with horizontally bedded shales, sand- 

 stones and occasional thin seams of coal. In a few separated 

 areas these coal seams are thick enough for profitable w'orking. 

 The extent of the unconformity between the Pennsylvanian beds 

 and the Devonian strata is revealed by the absence of the Upper 

 Devonian, the entire Mississippian, and the lower portion of the 

 Pottsville. 



The absence of these strata may be due to the fact that the 

 missing members were never deposited in this area, in conse- 

 quence of land conditions prevailing here during their deposition 

 elsewhere, but it is possible that at least a part of these members 

 were laid down, and afterward eroded before the deposition of 

 q§noj AJ3A 9q; qoiijAV 9DU3piA9 aifx "UHiuBAj.Csuuaj Suii(p9AO 91JJ 

 and broken Devonian surface affords tends to confirm this latter 

 view. 



The Devonian svstem of this area, the correlation of which is 



