86 
sinks and slightly Geveloped underground drainage may be considered as 
characteristic of the youth of subterranean drainage. There will be no 
collapse sinks at this stage. 
In the course of time the water of some of tbe streams may all pass 
below the surface and issue as great springs or subterranean streams in 
the channels of larger streams or in their own channels below where there 
may have been rapids er considerable fall in the beds. As time goes on 
this sinking of the water progresses headward along the stream, reducing 
Vig. 5. Abandoned bed of Lost River, near Lost River station, north of Paoli, 
Ind. During floods this channel contains water. It is twelve miles long. The val- 
ley is very broad, with indistinct bluffs. 
more and more of its course to underground drainage. The distance which 
streams may fiow underground before reappearing at the surface depends 
upon the physical conditions in which they are pliced. The distance that 
they are now observed to flow beneath the surface depends also upon the 
stage in the cycle of erosion in which they happen to be. Thus, in the 
Bristol-Standingstone region of ‘Tennessee and neighboring country the dis- 
tance seems te be about a mile. Lost river, in Indiana, flows about six 
niles in a direct line, or about double that distance by the old channel, be- 
fore reappearing. Perhaps Lost river sheuld be regarded as being in a 
somewhat later stage in its cycle than those of the region just mentioned, 
