266 S. K. EMMONS — OROGRAPHIC MOVEMENTS. 



on the Hayden map as Devonian and Carboniferous the lower part is known 

 to be Silurian and the upper part Triassic. If the upper Carboniferous is 

 not exposed it must have been overlapped, as on the eastern shores of the 

 Colorado island, by the succeeding Triassic sediments. 



In the wide area of the Uncompahgre plateau, to the west and northwest, 

 Triassic beds arc well developed, and the Carboniferous exposures represented 

 as resting directly on the Archaean are considered by Dr.Peale to belong to 

 the upper portion of this series. It would seem probable that these and the 

 similarly outlying regions of the Zuni plateau and the Nacimiento mountains 

 were island elevations in the early Palaeozoic seas over which no sediments 

 were deposited, and that after the late Palaeozoic movement they were de- 

 pressed below the sea level, since recorded observations seem to show that 

 continuous sedimentation went on over them from Carboniferous into Meso- 

 zoic time. 



< 'onclvMons mul Correlations. — Without a special examination of the region 

 with this object in view, it is difficult to make any satisfactory conjectures 

 as to whether the < !arboniferous beds at a given locality belong to those de- 

 posited before or after this movement, or whether both are represented. From 

 the present evidence it would appear that in the middle portion only of this 

 ion was the movement accompanied by any marked dynamic disturb- 

 ances, and that elsewhere it was in the nature of a parallel transgression. 



Again, while in the interior the aggregate thickness of the Palaeozoic beds 

 reaches from five to seven thousand feet, along the east Hanks of the Colo- 

 rado range, in the Laramie hills of Wyoming and the Black Hills of Dakota 

 their exposures rarely show more than seven or eight hundred feet of beds. 

 While it is certain that in the latter regions the lower Palaeozoic bed- are 

 represented, no evidence has yet been presented to show that upper Carbonif- 

 i rows horizons are exposed there; but the Triassic "Red Beds" are in most 

 cases characteristically developed. Palseontologically, Coal Measure forms, 

 which are abundant throughout the Carboniferous beds, cannot be consid- 

 ered characteristic of either Beries, and it is only those having a Permian 

 facie* thai afford definite evidence of the existence of the upper ( larboniferous 

 beds. On the other hand, in the Rocky Mountain region the lithological 

 characteristics, that furtherwesl serve to distinguish the beds carrying a Per- 

 mian fauna from the Carboniferous on the one hand and from the Trias on 

 the other, are wanting ; and there arc very con -idem I do thickni sses of beds 

 about which it can only be Baid that they were deposited Bomewhere in the 

 interval of time between the Carboniferous and Jurassic movements. What- 

 r r n : i \ be predicated in regard to the orographical history of this interval 

 i- nec< ssarily based upon data which are liable to be modified in the future, 

 and hence are very conjectural. It is, that the elevation accompanying the 

 movement was followed by an irregular subsidence, which was more pro 



