If a surface stream flows a long 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. 
