STRUCTURAL GEOLOGY 



411 



shown to be the case where an overfold passes into a reversed fault 

 (Fig. 332). Another type of thrust-fault is shown in Fig. 333. 



In thrust-faults, the heave is often great. The eastern face of 

 the Rocky Mountains near the boundary-line between the United 

 States and Canada has been pushed over the strata of the bordering 



Fig. 332. Diagram of a reversed or thrust fault. (U. S. Geol. Surv.) 



plains to a distance of at least seven or eight miles. 1 Overthrusts 

 of comparable displacement have been detected in Scotland, 2 and 

 elsewhere. 



Sometimes a fault branches, and sometimes the faulting is along 



Fig. 333. Diagrams showing relations of faults and folds. 



a series of parallel planes near one another, 3 instead of being along 

 a single plane. Such a fault is distributive (Fig. 37) . 



Faults are found to die out when traced horizontally, sometimes 



Willis, Bull. Geol. Soc. of Am., Vol. XIII, pp. 331-336, and McConnell, 

 Canada Geol. and Nat. Hist. Surv., 1886, Pt. II. 



2 Geikie, Text-book of Geology. 



3 Becker, Geology of the Comstock Lode, Mono. Ill, U. S. Geol. Surv., 

 Chapter IV. 



