o 
4-4 University of Kansas Geological Survey. 
“an irregular capping of Benton limestone on the north and west 
“sides. The east wall seems to be entirely sand. Wells sunk on 
“this ridge go through continuous sand until they strike the Dakota 
“sandstone at some distance below the surface level of the basin. 
“At the northeast corner of the bottoms there are several sandhills 
“similar in form to those on the south side of the Arkansas river. 
“In the region of this basin we find the upper part of the Dakota 
“formation, consisting of a layer of sandstone underlain by a thick 
“stratum of soft shales. Owing to the presence of considerable 
“quantities of salt and gypsum in these shales, Mr. W..N. Logan has 
“named them Saliferous Shales. He estimated their thickness at 
“about 30 feet. 
“In past time the two streams, Blood creek and Deception 
“ereek, which are the only streams of importance entering the 
“basin, probably flowed about as they do now. We suppose at one 
“time their channels were cut into the Benton and the Dakota sand- 
“stone. These materials resisting erosion quite well necessarily 
“made the deepening of their channels and the widening of their 
“valleys slow processes. But finally, having cut through these 
‘“narder strata to the softer stratum of saliferous shales beneath, 
“the processes of erosion were greatly increased, and it was there- 
“fore a comparatively short time until the streams had cut their 
“channels entirely through this stratum of shales to the harder layer 
“of sandstone beneath. They now began to widen their valleys, or 
“their valley; for the two streams probably united in one when this 
“shale was first encountered. This widening was likewise rapid, 
“so that a wide valley was soon formed. Had the sandstone over- 
“lying this shale bed been very hard we should doubtless have had 
“falls produced of about 30 feet in hight, which would have slowly 
“retreated up stream. There are good reasons for believing that 
“the point where the stream first encountered the shale bed was 
“considerably farther east than the present limits of the basin. 
“Kvidence of this is furnished by the fact that river sands cover 
“the surface for some distance in this direction. Thus the valiey has 
“been extending up stream as well as widening on either side. The 
“upper courses of the two streams mentioned have not even yet 
