FORMATIONS AND PHYSICAL HISTORY 



54i 



bodily at this time, though not to a great height. Without further 

 details, it may be said that enough is known to make it probable 

 that a large part of the continent was affected by deformative 

 movements of a gentle sort. 



Orogenic movements. The growth of mountains by folding 

 probably was in progress in the closing stages of the Cretaceous 

 period from Alaska on the north to Cape Horn on the south, more 

 than a quarter of the circumference of the earth. At the same time 

 folding movements probably affected the Antillean mountain sys- 

 tem, 1 between the southern end of the Cordilleran and the northern 

 end of the Andean systems, for in several of the Antillean islands 

 later formations rest unconformably on the deformed Cretaceous 

 beds. Where the Eocene rests conformably on the Laramie, the 

 disturbances of this time are not clearly distinguishable from those 

 of later date, which increased the folding initiated in this epoch. 

 Some of the folded ranges of the western mountains began their 

 history at this time, others had a new period of growth, and still 

 others date from a later time; yet the close of the Laramie was a 

 time of general erogenic movement in the western part of North 

 America. The Rocky Mountain system may be said to have had 

 its birth at this time. That these mountains are not older is shown 

 'by the deformation of the Laramie beds along with those of greater 

 age. That some of the folding was not younger is shown by the 

 lesser deformation of the Tertiary beds in the same region. 



Faulting. The growth of mountains at the close of the Creta- 

 ceous was accompanied by faulting on a somewhat extensive scale 

 throughout the region of movement, though the faulting of this time 



Fig. 457. 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. 



cannot be distinguished everywhere from that of later date. In 

 the Rocky Mountains of British Columbia, one overthrust fault has 

 been located which crowded the Cambrian rocks obliquely up over 

 the Cretaceous. The horizontal displacement is estimated to be 

 1 Hill, Nat. Geog. Mag., Vol. VII, p. 175. 



