371 



!in<l (■(tnso(Hi('iitl.v iiiiisf liavo ii iiiucli Iowit avcrajro jrradient. Those latter 

 stroains flow iivit fairly resistant rock. They ari' rather iK'euliar in that 

 they possess jiradients aitont ('((iial in all jxirtions of their eourses. The 

 gradient of lilne Kiver will he diseiissed in some detail helow. 



The general toiiograpliy of the hack-slojie portion of the euesta is largely 

 dependent iiiMin the rock in wliicii it is <lcvcl()pc(i. These regional features 

 dependent upon the rock iiaxc already liccn lirielly deserihed. For some 

 miles hack from the escarpment crest, the interstreani tracts reach up to 

 the preserved portions of the ui»lifted Tertiary peneplain. The main 

 streams have hroadly trenched this uplifted plain, and are from ItX) to 2r)0 

 feet lower. The interstreani areas are somewhiit beveled toward the main 

 streams, and fairly gentle slopes are the rule. Even in the Knohstone rocks 

 (these are the rocks on which the slopes are developed for .several miles 

 hack from the scarp), the valley slopes are fairly gentle. The exception is 

 along the line of Muddy Fork of Silver Creek, which is a special exception, 

 and will he discussed below. Where the regional rock is composed of the 

 llarrodshurg and Salem limestones, the slopes are long and gentle, and a 

 late maturity type of topography is generally prevalent. This sort of to- 

 pograiihy is excellently shown on the detailed topographic map in the 

 vicinity of Martinsburg. 



Farther west, in the region of the outcrop of the Mitchell limestone, the 

 toixigraphy has the api>earance of an uplifted siid<hole iilain. which it 

 probably is in part. This plain lias a westward slope of about 20 feet to 

 the mile. The uplift following the development of the Tertiary peneplain 

 permitted removal of waste material down to about the top of the St. Louis 

 limestone horizon. Drainage upon this rock is typically subterranean. But 

 it is probable that a portion of this plain is of base-level origin, as it in 

 part corresponds to locally developed plains elsewhere about 175 to 200 

 feet below the older and higher i>eneplain. Further uplift of the region 

 permitted the trenching of the plain by the main streams. Blue River and 

 Indian Creek receive few surface tributaries in their intrenched condition 

 in the sinkhole plain, or Mitchell plain. Lost River in its headwater area 

 flows over this hroa<l fairly level plain in a valley scarcely below the plain 

 itself. Farther west this stream sinks into the limestone and is lost to view 

 for some 10 miles. From the place where it sinks to where it appears again 

 at the surface it makes a descent of al)out 125 feet. The old surface channel 

 is present. There is little doubt but that uplift was a factor in bringing 

 about this subterranean condition. Distinct evidence is at hand showing 

 that this subterranean space of Lost River has been progressively made 

 longer and longer, and it is i)robable that sinks will continue to develop in 

 the streaui farther u)) than the i)resent siidc with a resultant abandonTuent 

 of the present one. 



Approximately one-half of the Mitchell limestone area above the general 

 ground-water table is partly covered by clastic Chester strata. The 

 Chester occurs as ridges and isolated hills which rise high above the flat 

 spaces of the Mitchell limestone areas. The.se hills reach approximately 

 to the elevation of the uplifted Tertiary peneplain, attaining heights of 



