788 



PRINCIPLES OF STRATIGRAPHY 



end of each tooth-like projection is dissolved away — the hollows are 

 deepened, and thus the teeth, by gliding under pressure, penetrate 

 deeper and deeper into the opposite bed, while at the same time 

 they become longer by the deepening of the hollows which surround 

 and isolate them. The residual clay, left on solution, comes to rest 

 as a cap on the top of the stylolite, protecting this top from solu- 

 tion. 



It is not necessary that the suture or dividing plane should be 

 irregular to begin with. Unequal solution on opposite sides of the 

 plane is sure to occur, since rocks are seldom so homogeneous that 

 all parts are equally soluble. Such irregularity once produced, it 

 will continue to be augmented, for the greatest amount of pressure 



Fig. 173. Sketch of a portion of a limestone face of white Jura ^ in Tal- 

 heim, showing styloHtes. (After Wagner.) The spaces result- 

 ing (black) are filled with calcite. (After Wagner.) (Much 

 reduced.) 



will occur where the rocks on opposite sides come in contact. The 

 projecting mass, especially if it is crowned by a fossil which is less 

 readily soluble than the enclosing rock, generally suffers the least 

 solution, while the hollow opposite into which it presses suffers 

 the largest amount of solution. The protecting cap of clay also 

 helps this process. The sides of the growing teeth are free from 

 pressure, so solution is absent here, and deposition even may oc- 

 cur. (Figs. 171-173-) 



The length of the individual stylolite tooth serves as a fair meas- 

 ure of the amount of material removed by solution from both sides 

 of the fracture plane. 



II. Cone in Cone. This is a structure sometimes found in 

 lutaceous rocks, particularly in calcareous or ferruginous argil- 

 lutytes. It consists of a number of crenulated or corrugated conical 



