Bui. 502, U. S. Dept. of Agriculture, 



Plate II. 



• ^c>%--," ^ ^->^ J^^ 



1*^ 



•^^fcS...w 





Fig. 1.— Side of an Irrigation Ditch, Showing Nearly Vertical Cleavage Planes. 



FiQ. 2.— Shales Having Nearly Horizontal Layers which have be^n Cut by 

 Cleavage Planes Caused by Great Pressure. 



Cleavage planus continuous through shalo layers aud intervening roek strata. 



