24 



SOIL PHYSICS AND MANAGEMENT 



to cave regions. These sinkholes or basins vary in size from ten to 

 two hundred feet or more across and from three to fifty feet in 

 depth (Fig. 14). They vary in frequency as well as size. In some 

 localities there are only a few small ones that are not objectionable, 



Fia. 14. Sinkholes in a cave region Southern Illinois. The bottoms of the sinkholes are 

 still occupied by brush. (H. C. Wheeler.) 



while in other regions they are so large and frequent that the land 

 is entirely worthless for cultivation. When the outlet from these to 

 the cave becomes clogged, "sinkhole ponds" result (Fig. 15). In 



. ' . ' 



Fio. 15. The outlets of sinkholes sometimes become clogged and "sinkhole" ponds 

 result. (H. C. Wheeler.) 



