86 



sinks and slightly develoiied nuderground drainage niaj' be considered as 

 characteristic of the yoiith of subterranean drainage. There will be no 

 collapse sinks at this stage. 



In the course of time the wat^- of some of the 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 or considerable fall in the beds. As time goes on 

 tliis sinking of the water progresses headword along the stream, reducing 



l''ig. 5. Abandoned bed of Lost River, near Lost liiver station, uortli of I'aoli, 

 Ind. During- floods this cliannel contains- water. It is twelve miles long. Tlie val- 

 ley is verj' broad, with indistinct bluffs. 



more and more of its course to underground drainage. The distance which 

 streams may flow underground before reappearing at the surface depends 

 upon the physical conditions in which they are pbiced. The distance that 

 they are now observed to How beneatli the surface depends also upon tlH> 

 stage in the cycle of erosion in wiiich they happen to be. Thus, in the 

 Bristol-Standingstone region of Tennessee and neigiiboring country the disr 

 tance seems to 1)0 about a mile. Lost river, in Indiana, flows about six 

 miles in a direi-t lin(\ oi' alinni double lliat distance by the old cMnuel, he- 

 fort- reapp<'a)'ing. I'erliaps Losl river slnadd ))e regarded as being in a 

 ,souievthat later stage in its cycle than those of the region just mentioned, 



