Lost River - Karst Information Portal

2007 NSS Convention Guidebook
84
Figure 7. Map showing the location of Harrison and Crawford counties relative to the Illinois Basin
and Cincinnati Arch (modified from Sunderman, 1986).
by hundreds of sinkholes per square mile, with
over 1,022 sinkholes counted per section in
some areas (Malott, 1945, pp 12–l3). The
Mitchell Plain south of the river can be further
subdivided: the sinkhole plain proper lies on
the west margin, adjacent to deeply entrenched
surface drainage and cavernous drainage, while
the east side is characterized by surface streams
flowing across it. Caves have developed to a
lesser degree in the eastern portion of the plain.
The eastern boundary of the Mitchell Plain with
the Norman Upland is transitional, but the
boundary of the soil-mantled surface drainage
plain with the sinkhole plain is generally abrupt
and commonly the site of sinking streams (for
example the Lost River).
The soils of the Mitchell Plain, including
the so-called “terra rosa” consist of a sequence
of residues from limestone and clastics; alluvial
clays, sands, silts, and gravels; lag gravels; and
loess and paludal deposits ranging in age from
Tertiary to Recent. (Powell, 1971; Powell and
Thornbury, 1967, pp 16–17; Ruhe, 1974;
Olson, 1980; Hall, 1976; Ruhe and Olson,
1980). The Mitchell Plain was mantled with
these materials, excluding the loess, to an
estimated average thickness of 30 feet prior
to the time of development of the Blue River
Strath, probably during the late Tertiary. The
soils were dissected by surface streams and
sapped through karst drainage systems to
evolve into essentially the present landscape
prior to emplacement of thin loess of Illinoian
and Wisconsinan ages. The sinkhole character
of the Mitchell Plain is evident as a widespread
zone along the western margin of the sinkhole
plain where the soils have been removed by
sapping, slumping, and piping. The eastern