103 



lapse and the return to surface drainage. Briefly, it may be stated that 

 the cycle is : surface drainage, partial subterranean drainage, and a re- 

 turn to surface drainage. The final state is peneplaiuitioii or base leveling. 



.5. In youth and maturity nearly all the sinks are solution sinks. 



G. In old age many of the sinks are formed by collapse. Solution 

 sinks may finally be transformed into sinks of collapse. 



7. Surface streams resting on a plain of soluble rocks with streams 

 at lower levels bordering them may have their waters diverted by subter- 

 ranean capture. 



8. Piracy probably takes place between subterranean streams and 

 between parts of the same stream. 



Bloom i II gtoii, Indiana. 



References to the "eai-Iy pleistocene" iieacplain in this paper sliould read "late 

 tertiary (?)," since the cycle was interrupted at about the close of the tertiary or 

 beginning of the pleistocene period. 



