THE JURASSIC PERIOD. 69 



is not to be understood that the Sierras and Klamaths attained moun- 

 tainous heights immediately at the end of the Jurassic period, or that 

 they have not had subsequent periods of growth. In the Klamath 

 Mountains, for example, there are deformed beds of late Tertiary age. 

 It is probable that the Coast Range of California began its history 

 at the same time, for deformed Jurassic beds (Golden Gate series) 

 underlie the Lower Cretaceous unconf ormably in the axis of the range ; * 

 but the movements which gave the Coast Range its present form, or 

 its present form as modified by erosion, took place at a much later 

 time. 



Farther east, the Humboldt ranges of Nevada are thought to have 

 been started in their development at about the same time as the ranges 

 already mentioned. More than 20,000 feet of Jurassic and Triassic 

 strata are involved in their folds. It is possible that other mountains 

 of the west, the cores of which had been islands throughout the Triassic 

 and Jurassic periods, were affected by renewed uplift at this time of 

 general disturbance. The orogenic disturbances at the close of the 

 Jurassic may have been comparable in kind and in extent to those 

 which affected the continent at the close of the Paleozoic, but they 

 were probably of a lower order of magnitude. The disturbances which 

 have been definitely referred to this period were certainly less extensive, 

 and less intense. 



The position and relations of the Jurassic formations at various 

 points in the west are shown in Figs. 351 to 354. 



Changes in geography. — At the close of the Jurassic, geographic 

 changes equal in extent to those of the closing stages of the Paleozoic 



Fig. 351. — Section showing the relations of the Jurassic system near Telluride. Colo. 

 Td, Triassic (Dolores formation); Jme, Jurassic (?) (McElmo formation); Kd and 

 Kmc, Cretaceous (Dakota and Mancos formations) ; Esm, Eocene (San Miguel 

 formation); dm and gd, igneous intrusions. (Purington, U. S. Geol. Surv.) 



are not recorded; yet the changes were great, though in regions less 

 well known than those affected by the deformative movements which 

 occurred late in the Paleozoic era. Much, if not all, of the great Upper 



1 Fairbanks, Jour. Geol.. Vol. Ill, pp. 415-430, and Smith, Bull. Geol. Soc. of Am., 

 Vol. 5, pp. 257-8. 



