256 



PHYSICAL GEOLOGY 



distances, but is either gently arched, or dips and pitches, the 

 slant of the axis being called its pitch (Figs. 244, 245). 



One sometimes sees 

 anticlines unaccom- 

 panied by synclines, 

 but more often the 

 two occur together. 

 Notable examples of 

 series of great parallel 



folds are to be seen in 

 Fig. 246. — An anticlinonum. (After J. (jeikie.) 



the Appalachians of 

 Pennsylvania and in the Juras of Switzerland. In greatly folded 

 regions, indeed, the conspicuous anticlines may be considered as minor 



Fig. 247. — The Mt. Greylock, Massachusetts, synclinorium. (U. S. Geol. Surv.) 



crumplings of a great, complex anticline (Fig. 246) called an anti- 

 clinorium, or of a complex syncline called a synclinorium (Fig. 247). 

 A form of fold which, though simple, cannot be included in the term 

 anticline is the monocline, 

 or step-fold (Fig. 248). /~~ 



It occurs where horizon- 

 tal rocks suddenly bend 

 downward. In portions 

 of Utah and Arizona 

 monoclinal folds are not 

 uncommon and often 

 merge into or give place 

 to faults. 



Effect of Folding on 

 Competent and Incom- 

 petent Strata. — If the Fig. 248. — M 



onocuna 



linal flexure and fault. 



