518 



GEOLOGY. 



overthrust. In such cases the throw is to be distinguished from the 

 stratigraphic throw (see Fig. 426). 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 



\. 



Fig. 426. — Diagram of a thrust-fault illustrating the several terms used in describing 

 faults. The distinctions between heave and displacement, and between throw 

 and stratigraphic throw, are to be especially noted. (Willis, U. S. Geol. Surv.) 



/^-v.-^ - 



Fig. 427.— Step-fold shd-vying (in 1) break in the massive limestone bed which de- 

 termines the plane of the break-thrust along which the displacement shown in 2 

 takes place. (Willis, U. S. Geol. Surv.) 



strata of the bordering plains to a distance of at least eight miles.^ 

 Overthrusts of like gigantic displacement have been detected in British 

 Columbia,^ Scotland,^ and elsewhere. 



Sometimes a fault branches (Fig. 428) and sometimes the faulting 



' WiUis. Bull. Geol. Soc. of Am., Vol. XIII, pp. 331-336. 



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



'Geikie. Text-book of Geology. 



