NO. 4 PHYSIOGRAPHY OF ROCKY MOUNTAINS LEE / 



or of Permian age, but it is of primary importance that highlands 

 were formed where the open sea had been, and that south and east 

 of these highlands lay shallow basins in some of which beds of salt 

 and gypsum were formed. In other places continental deposits 

 accumulated. These consist chiefly of coarse sand with conglomerate 

 in many places. Obviously a large proportion of the red sediments 

 were derived from highlands situated essentially where the Rocky 

 Mountains now stand. These gypsiferous " Red Beds " (the Man- 

 zano) of New Mexico and beds of the same age elsewhere, are here 

 regarded as Permian, and the question naturally arises : Are these 

 beds correctly included in the Carboniferous system or should they 

 constitute a separate system? On the principle that the first well- 

 defined movement in a major orogenic disturbance opens a new geo- 

 logic period and inaugurates a new system, this question becomes per- 

 tinent, for there is little doubt that a notable orogenic movement pre- 

 ceded the formation of the Permian " Red Beds." This question 

 appears all the more pertinent when we reflect that in few places in the 

 Rocky Mountain region can a line of separation be drawn between 

 Permian and Triassic rocks. Even in places like the Grand Canyon 

 region, where marine invertebrates occur, the fossils once described as 

 Permian are now said to indicate Triassic age. In brief, so far as 

 now known, there is a much greater break in sedimentation between 

 the Pennsylvania!! limestone and the Permian " Red Beds " than 

 there is between the latter and the rocks now classed as Triassic. 



TRIASSIC PHYSIOGRAPHY 

 UPLIFT AND EROSION 



Whatever may be the final answers to the questions just raised, it 

 is obvious that previous to the formation of rocks now called Trias- 

 sic, there were highlands in the Southern Rocky Mountain region, 

 although their original volume had been greatly reduced by the 

 removal from them of great quantities of the detritus which con- 

 stitutes the older " Red Beds." Also, the greater part of the North 

 American continent was above sea-level, for only small parts of it 

 are now occupied by Triassic rocks of marine origin. 



The sedimentary rocks of Triassic age in some parts of the 

 Southern Rocky Mountains have not been differentiated from the 

 older rocks. But those of undoubted Triassic age are non-marine 

 and are classed as Upper Triassic, such as the Shinarump con- 

 glomerate and Chinle formations of northern Arizona, and their 

 equivalents in neighboring regions. The land from which the sedi- 



