THE CRETACEOUS PERIOD. 163 



from Alaska on the north, to Cape Horn on the south, more than a 

 quarter of the circumference of the earth. Similar movements prob- 

 ably affected the Antillean mountain system, 1 lying between the south- 

 ern end of the Cordilleran and the northern end of the Andean systems, 

 for in several of the Antillean islands, later formations rest unconf orm- 

 ably on the deformed Cretaceous beds. Locally, as 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 deformation initiated at this time. Some of the folded ranges 

 of the Cordilleran system began their history at this time; others had 

 a new period of growth, and still others date from a later period. Yet 

 the close of the Laramie was, par excellence, the period of orogenic 

 movement in the western part of North America. The Rocky Mountain 

 system may be said to have had its birth at this time. That the exist- 

 ing mountains are not older is shown by the deformation of the Lara- 

 mie beds along with those of greater age. That this folding was not 

 younger is shown by the lack or slightness of deformation of the Ter- 

 tiary beds in the same region. 



North of the United States, the site of the Laramide range (the 

 continuation of the Rockies of the United States) had been a tract of 

 great deposition through Paleozoic and Mesozoic times. In it, sedi- 

 mentary beds had accumulated to a thickness, which, by the usual 

 methods employed in such cases, is estimated at 50,000 feet. 2 At 

 this time the strata, doubtless already inclined and bowed as inci- 

 dents of deposition, were tilted, folded, and faulted into the Lara- 

 mide range. The thrust producing the folding and faulting appears 

 to have come from the west, as implied by the position of the over- 

 thrusts. The height of the mountains developed in this region at 

 this time is estimated at 20,000 feet. The mountains have since 

 undergone further elevation, and had erosion not reduced them, it is 

 estimated that their present height would be 32,000 to 35,000 feet. 

 It has been calculated that in the Laramide range a surface belt 50 

 miles wide was reduced to one hah that width. 3 Estimating the aver- 

 age height of the faulted tract at about half the maximum height, 



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



2 Dawson, Science, Vol. XIII, 1901, p. 401, and Bull. Geol. Soc. Am., Vol. XII, 

 p. 88. 



3 Dawson, Bull. Geol. Soc. Am., Vol. XII, p. 87. 



