92 



If a surface stream flows a ioiig distance over a rather gentle grade to 

 reach a certain level while a competitor flows a short distance to reach 

 a similar level it may capture the headwaters of the former through sub- 

 terranean drainage, leaving the divide between the valleys intact. This 



Fig. 11. Emergence of cave stream, mouth of Shawnee cave east of Mitchell, 

 Indiana. The roof of the cave at its mouth is well supported. Just back of this 

 there are two large rooms connecting with the main cave, leaving a large area of 

 roof unsupported. It has faulted down about six inches. The completion of this 

 collapse might, in time, leave a natural bridge at the present mouth of the cave. 

 The valley is a typical collapse valley. 



