90 
but with a fairly wide bottom and a blunt, steep termination at their heads. 
In these respects they resemble miniature glaciated valleys. When well de- 
veloped they may be shown on accurate topographic maps. Surface erosion 
begins modifying them at once and finally obliterates the evidence pointing 
to their origin. The final result of the subterranean drainage cycle is thus 
a surface drained peneplain. 
There is a lack of subterranean drainage in the old age stage of the 
eycle in the Bloomingten region. The whole sink hole plain of Indiana 
Fig. 9. More distant view of Leonard's Spring. ‘he main spring is seen back 
of the stone dam. ‘The water is issuing from a hole in the dam in the middle fore- 
ground. Note the steep, biunt end of this collapsed-cave valley. 
may be considered as in its maturity. Mowever, there are exposed in the 
sides of the monadnocks west of Harrodsburg certain old solution channels 
which probably represent the very heads of the subterranean channels of 
the preceding cycles of erosion. Indeed it is not improbable that the 
streams tributary to Clear creek on the west and north of Harrodsburg 
owe their present position in some degree to the location of former sub- 
