214 GEOLOOY. 



mountains worn certainly not so high as now, though considerable 

 elevations and great relief must have existed to furnish the abundant 

 sediments. 



Close of the Eocene in North America. — The closing stages of the 

 Eocene were marked by crustal movements in the west, resulting in 

 considerable changes in geography. Such movements had been in 

 progress throughout the period, as has been indicated, but the changes 

 at the close were on a larger scale. The deformative movements 

 seem to have included faulting and folding, as well as general crustal 

 warping. The results of these movements were the withdrawal of 

 the sea from the lands which it had covered along the Pacific coast, 

 and the development of new areas of high and low lands, and there- 

 fore a shifting of the areas of rapid degradation and aggradation. 

 Among the deformations connected with the close of the Eocene were 

 the renewed upbowing of the Klamath mountains, 1 the beginning 

 of the development of the Coast range of Oregon, 2 and the notable 

 deformation (folding) of the newly deposited sediments in central 

 Washington, 3 and in the Santa Cruz mountains of California. 4 In 

 and about the Basin region, 5 faulting, rather than warping and 

 folding, seems to have been the prevalent phase of deformation, though 

 the faulting at the close of the Eocene is not always separable from 

 that of later times. In Colorado, deformation at the close of the 

 Eocene is recorded at numerous points, 6 with the general result that 

 degradation succeeded aggradation in some places, while the change 

 was reversed in others. Faulting and warping also seem to have 

 occurred in New Mexico and Arizona at about the same time, resulting 

 in changes which stimulated erosion in those regions in the epoch 

 which followed. These crustal movements seem to have been con- 

 nected, in more than an accidental way, with an increase in the vigor 

 of igneous activity, as shown by the extrusions of abundant igneous 

 rock near the close of the period. 



Outside the Cordilleran region there were lesser changes. Along 

 the Atlantic and Gulf coasts the Miocene is in many places uncon- 



1 Diller, BuU. 196, U. S. Geol. Surv. 



2 Diller, Port Orford, Ore., folio, U. S. Geol. Surv. 



3 Smith (G. O.), Mount Stuart, Wash., folio, U. S. Geol. Surv. 



4 Ashley, Jour, of Geol., Vol. Ill, p. 434 et seq. • 



5 Dutton, Mono. II, U. S. Geol. Surv., and King, op. cit., p. 541. 

 8 See Colorado folios of the U. S. Geol. Surv. 



