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and consequently must have a much lower average gradient. These latter 
streams flow over fairly resistant rock. They are rather peculiar in that 
they possess gradients about equal in all portions of their courses. The 
gradient of Blue River will be discussed in some detail below. 
The general topography of the back-slope portion of the cuesta is largely 
dependent upon the rock in which it is developed. These regional features 
dependent upon the rock have already been briefly described. For some 
miles back from the escarpment crest, the interstream tracts reach up to 
the preserved portions of the uplifted Tertiary peneplain. The main 
streams have broadly trenched this uplifted plain, and are from 100 to 250 
feet lower. The interstream areas are somewhat beveled toward the main 
streams, and fairly gentle slopes are the rule. Even in the Knobstone rocks 
(these are the rocks on which the slopes are developed for several miles 
back 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 be discussed below. Where the regional rock is composed of the 
Harrodsburg and Salem limestones, the slopes are long and gentle, and a 
late maturity type of topography is generally prevalent. This sort of to- 
pography 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 
topography has the appearance of an uplifted sinkhole plain, which it 
probably is in part. This plain has 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 peneplain. 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 broad 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 about 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 probable that sinks will continue to develop in 
the stream farther up than the present sink with a resultant abandonment 
- 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. These hills reach approximately 
to the elevation of the uplifted Tertiary peneplain, attaining heights of 
