APPALACHIAN AND CORDILLERAN MOVEMENTS CORRELATED. 26'J 



nounced in the interior region, but in the outlying region was followed by- 

 further subsidence in Triassic time, as a result of which the earlier beds were 

 overlapped to such an extent by the Triassic sandstones that they have rarely 

 been exposed by later movements or erosion. 



In the Wasatch and Uinta regions, the upper Carboniferous and Permian 

 are undoubtedly represented. If I am right in considering that only the upper 

 members of the Carboniferous are represented in the Uinta range, it would 

 become probable that the erosion observed by Powell iu the canon of Green 

 river on the beds underlying the Carboniferous was produced during the eleva- 

 tion that accompanied this movement. 



With regard to the broader and more continental elevations, the fact that 

 over the Palaeozoic continent of Utah and Nevada, as well as over the great 

 Appalachian continent, not only Mesozoic but also Permian beds are wanting, 

 would indicate an alternate movement between those regions and the Rocky 

 Mountains — that is, that during the Carboniferous elevation of the latter these 

 still remained below the level of sedimentation, though shallow-water condi- 

 tions prevailed to a certain extent, but that, while in the Rocky Mountain 

 region subsidence continued into the Trias, the continents on either side reached 

 a permanent elevation at the close of the Carboniferous time which was so far 

 maintained that the waters of the ocean never again invaded them. 



A similar condition, according to present evidence, would seem to have 

 obtained in northern Mexico ; for Dr. White* considers that south of the 34th 

 parallel no Trias or Jura exists, but that the marine lower Cretaceous (which 

 also includes possible representatives of the Atlantosaurus beds) rests directly 

 upon the Carboniferous. 



The Jurassic Movement. 



The succeeding orographic movement of the region, which was even more 

 widespread and more marked iu its effects, has been designated the Jurassic 

 movement, because the first beds deposited after it were those containing the 

 vertebrate fauna determined by Professor Marsh to be of late Jurassic age, 

 and called by him " Atlantosaurus beds." A somewhat meagre fresh-water 

 molluscan fauna, considered by Dr. White as also of late Jurassic age, has 

 been found by him in the Atlantosaurus beds of the eastern flanks of the 

 mountains, and by Mr. Eldridge in beds corresponding stratigraphically and 

 lithologically with these on the west flanks in the Elk mountain region, where 

 the dynamical effects of the movement are most marked and have been most 

 carefully studied. The beds which in the Rocky Mountain region are char- 

 acterized by this fresh-water Jurassic fauna are generally very thin, contain 

 as a rule but scanty remains of organic life, and want the persistence and 



* Am. Journal Sci., 3d ser., Vol. XXXV1I1, 1889, p. 440. 



