252 : 3 
THE SINK-HOLE REGION, 
Overlying the Knobstone group are the thick beds of Lower Carbonifer- 
ous limestones, in which are found the caverns of southern Indiana. This 
limestone region is completely pitted with sink-holes, and practically the 
whole of its drainage is by underground channels. This region has a 
gradual westward slope. It is the sink-hole region of Indiana. There is 
a noticeable increase in the size of the sink-holes in going from east 
to west as the limestone beds become thicker. 
THE WESTERN PLATEAU. 
West of the sink-hole region formed by the limestones, is the very 
rugged region to be found immediately east of the Coal Measures. The 
hills of this region are capped by the Mansfield sandstone or Mill-stone 
grit, to which formation they are in large part due. The region in which 
the Mansfield sandstone is the controlling formation may be termed the 
western plateau. This plateau has been very much dissected by its 
streams. 
THE WESTERN LOWLAND. 
Overlying the Mansfield standstone are the soft and easily eroded beds 
of the Coal Measures. These beds have been already worn down very 
near to their base level of erosion, if indeed they have ever been much 
above that level. 
CONCLUSION, 
(a.) In passing from east to west across southern Indiana, three prom- 
inent topographic features are crossed, and these features are the results 
of combinations of strata as follows: (1) the high eastward escarpment 
along the Ohio River caused by a thick series of easily-eroded calcareous 
shales overlain by thick and resisting limestones; (2) the high eastward 
facing escarpment with its outliers to the east, known as the “Knobs;” 
this escarpment is the result of a thick series of soft clay and sandy 
shales, protected by sandstones and resisting limestones. Along the line 
under discussion this escarpment is 28 miles west of the escarpment 
along the Ohio; (8) the high hills of Martin County, which are the result 
of a series of limestones and sandstones capped by more resisting sand- 
stones and which do not rise as an escarpment from the east, but become 
