UrPER WYOMING FORMATION. 21 



A portion of the beds included in this division have hitherto been 

 classed in the succeeding Morrison group, or Jurassic, but as they contain, 

 so far as observed, no fossil remains, the Hallopus fauna which occurs near 

 Canyon City not having been detected in tins region, the line of division 

 has been drawn on grounds of lithological composition and structure. In 

 lithological composition the variegated shales resemble similar beds be- 

 longing to the Jurassic on the western slopes of the mountains, but the 

 structural evidence was what finally determined Mr. Eldridge to draw 

 the line where he did. This point will be discussed later. 



JURASSIC MOVEMENT. 



A widespread orographic movement, resulting in elevation and erosion, 

 and in some parts accompanied by folding and faulting-, took place in the 

 Rocky Mountain region previous to the deposition of the series of beds 

 which, from their containing vertebrate remains, have been considered as of 

 late Jurassic age. This has been designated the Jurassic movement, since 

 its effects were most apparent during that period, though it may have been 

 inaugurated toward the (dose of the Trias, when shallow water and in some 

 places lacustrine conditions prevailed. As a result of this elevation, the 

 marine deposits of Jurassic age, the Baptanodon beds of Marsh, which 

 were formed in the regions to the north and west, were shut out from the 

 Rocky Mountain region of ('(dorado, and during the depression which fol- 

 lowed only fresh-water beds were laid down in this region; the character 

 of the fossil remains found here indicates thai oceanic waters did not enter 

 the region until Dakota time, or at the commencement of the Upper Cri ta- 

 ceous cycle of deposition. 



A notable feature in the Jurassic movement, deduced from the evidence 

 which present conditions afford, is that the folds produced bv it were in 

 general at right angles to those formed by succeeding and more pronounced 

 movements; therefore, after the crests of folds have been planed off by ero- 

 sion and a later series of beds deposited over their upturned edges, when the 

 whole complex is again folded at right angles to the earlier folds and again 

 eroded, the unconformity between successive series is shown in the result- 

 ing outcrops by discrepancies in strike rather than in dip of beds. This 



