THE OROGENIC EPOCHS IN NORTH AMERICA 645 



Throughout this great belt, which doubtless has extensions 

 in Asia on the west and also in South America, the folding was 

 accompanied or followed by the intrusion of enormous masses of 

 granitic rocks, the commonest types among which are granodiorite 

 and quartz-diorite. In the intensity of the folding there was much 

 variation, but through California and Washington, at least, it was 

 great. 



Although nearly all writers on the subject agree in assigning 

 this epoch of diastrophism to the Jurassic period or its close, there 

 is considerable difference of opinion as to a more precise date. The 

 Alaskan geologists have usually referred it to the middle Jurassic. 

 Stanton and the earlier Californian geologists assigned it to the end 

 of the Jurassic. According to J. P. Smith it took place just before 

 the Portlandian epoch of the late Jurassic. These differences of 

 opinion are probably in large part due to the difficulty of correlating 

 the faunas of such widely separated countries as California, Alaska, 

 and Europe, rather than to any real difference in the date of the 

 disturbances in the several regions. 



Oregonian orogeny {post-Comanchean). — In the literature of 

 Pacific coast geology there is much evidence to indicate that the 

 deposition of the Shasta and related series (Comanchean) was 

 followed by crumpling of the strata, accompanied by the intrusion 

 of igneous rocks, especially peridotitic varieties, now changed to 

 serpentine. The phenomena have been found interruptedly from 

 southern Mexico through California, Oregon, and Washington to 

 southeastern Alaska. In all cases they lie near the coast, and in 

 no instance are they known to occur east of the area affected by the 

 Nevadian orogeny. As in that preceding orogenic epoch, so here, 

 the folds appear to be roughly although not exactly parallel to the 

 edge of the Pacific basin. In most districts the folding was of 

 moderate intensity but in southwestern Oregon the Comanchean 

 strata stand on edge in isoclinal attitude. 



All inferences as to a period of deformation between the lower 

 and the upper Cretaceous necessarily rest upon the correlations of 

 the strata involved. On the whole, the Comanchean and Cre- 

 taceous beds of the Pacific province are only sparingly fossiliferous 

 and many of the species, such as Aucella, are of large vertical range 



