BAIN.] TOPOGRAPHY GEOLOGY. l7 



walls for the greater part of its course. At 345 feet there is at several 

 points a wide development of bottom land, as at Elizabethtown, Rosi- 

 clare, and near the mouth of Lusk Creek at Golconda. From Bay 

 City the low land extends west in a broad belt, known as the Bay 

 Bottoms, to Cache Eiver, in Johnson County. In periods of flood an 

 independent connection between the Ohio and Mississippi rivers is 

 established by this route. At Rosiclare the bottom is likewise subject 

 to overflow. The Ohio makes the impression of being very imper- 

 fectly adjusted to its valley. The great Bay Bottoms cut directl}^ 

 through the upland, but are traversed by only insignificant streams, 

 while at various points along the Ohio the valley seems none too 

 large for the stream. The arrangement of tributaries is also erratic. 

 Near the mouth of Grand Pierre Creek are tributaries which head 

 within a few feet of the Ohio, but flow northward and by a rounda- 

 bout way into the minor stream. There are no topographic maps of 

 the region and no good drainage maps, so that it is unsafe to make 

 many generalizations. It seems clear, however, that the streams are 

 poorly adjusted and that they show evidence of superposition. Their 

 courses were for the most part determined when the present upland 

 was a lowland, and with its uplift they have cut directly downward 

 without much adjustment through hard and soft rocks alike. The 

 most important tributaries of the Ohio — Big Creek. Grand Pierre 

 Creek, and Lusk Creek — have cut back across the upland until their 

 headwaters are at work upon the south slope of Karbers Ridge. At 

 several places the tributaries of these streams on the south and those 

 of the Saline River on the north have cut entirely through the ridge, 

 forming passes or gaps. Packers Gap, near the headwaters of Grand 

 Pierre Creek, is one of the best known. 



GEOLOGY. 



GENERAL STATEMENT. 



Both igneous and sedimentary rocks occur in this district. The 

 former are represented in a number of dikes found near the Ohio 

 River and are all, so far as known, of the same general class of 

 rocks. The sedimentary formations represent four different sys- 

 tems — Devonian, Carboniferous, Tertiary, and Quaternary. The 

 Devonian outcrops are confined to a limited area in northern Hardin 

 County; the Tertiary gravels are found only in southern Pope 

 County; the Carboniferous occupies the larger part of the terri- 

 tory, while the loess loam of the Quaternary extends as a thin 

 mantle over the whole. The Carboniferous rocks consist for the 

 most part of fonnations belonging to the Mississippian series, the 

 Mansfield sandstone alone representing the Pennsylvanian. In the 

 Bull. 255—05 M 2 



