754 GEOLOGY 



movements probably affected the Antillean mountain system. 1 

 between the southern end of the Cordilleran and the northern end 

 of the Andean systems, at the same time, for in several of the An- 

 tillean islands later formations rest unconformably on the de- 

 formed Cretaceous beds. Where the Eocene rests conformably on 

 the Laramie, the disturbances of this time are not clearly distinguish- 

 able from those of later date, which increased the folding initiated 



Fig. 510. Section in northern Montana, showing Proterozoic rock. A, 

 thrust over Cretaceous, K. Subsequent erosion has removed much of 

 the overthrust beds, but Chief Mountain is a remnant of them. The 

 extent of the overthrust is unknown. 



Fig. 511. Chief Mountain. (Willis, U. S. Geol. Surv.) 



in this epoch. Some of the folded ranges of the western mountains 



began their history at this time, others had a new period of Drouth, 



and still others date from a later time; yet the close of the Lnnmiie 



i time of general orogenic movement in the western part of 



1 Hill, Nat. Geog. Mag., Vol. VII, p. 17.'.. 



