176 



PRINCIPLES OF STRATIGRAPHY 



by sink-holes, and sometimes by depressions filled intermittently 

 with water. That all large caverns are the result of solution of 

 solid limestone masses has been seriously questioned. Walther 

 (42:^60} has called attention to the fact that large dome-like cham- 

 bers are commonly found in reef -like masses of limestone and that 

 these are covered with stalactic deposits, showing that def)osition and 

 not solution has been active here for a long period of time. He sug- 

 gests that many of these may be original hollows in the reef masses, 

 such as are known to occur in structures of this type. 



No minerals are wholly insoluble in the ground water solutions, 

 even quartz, the most resistant, being at times attacked by moisture- 

 carrying solvents. (Hayes-14.) 



Fig. 25. Karren or /fl/'/a^ (rascles-) topography of the Sentis formed by solu- 

 tion by surface streams on a limestone plateau. (After Heim.) 



While solution is most characteristic of the belt of weathering, it 

 is, nevertheless, not confined to it. Active solution goes on in the 

 belt of permanent ground water, but it is here balanced by equally 

 active deposition. Streams and rain water form a rough solution 

 topography on limestone plateaus. These are illustrated by the 

 Karren or lapiaz of the Sentis. (Fig. 25.) 



Cementation. This is of equal importance with solution in the 

 belt of cementation, forming one of the characteristic processes of 

 this belt. It is practically unknown in the belt of weathering. The 

 material deposited is largely derived from the belt of weathering, 

 and the result of such deposition is the partial closing of the pore 

 spaces in the rock below the level of ground water. The expan- 

 sion of the minerals on hydration further tends to close up these 

 pores. The ultimate result of these processes will be the induration 



