194 J. D. Dana — Rocky Mountain Protaxis and the 



eastern margin of the emerged Great Basin, that is, the coast 

 region of the eastern Mesozoic seas, in which the Triassic, 

 Jurassic and Cretaceous rocks were formed ; and if so, the 

 Wasatch Archaean was not within the subsiding area over 

 which Mesozoic sediments were laid down, but part of the 

 more stable outside region, like the Archaean protaxis north of 

 the United States boundary. 



While regarding with admiration the survey of the Fortieth 

 Parallel, and adopting many of the conclusions presented in its 

 Reports, it seems reasonable to hesitate here, so far at least as 

 to pass in review the bearings on the geological history of the 

 region of this modification of its views ; and I therefore pro- 

 ceed to state the sequence of events which appears to be indi- 

 cated by the reported facts. 



1. At or near the close of the Paleozoic, when the area of 

 the Great Basin lying to the east of the meridian of 117|- W. 

 emerged, placing its latest Carboniferous rocks more or less, 

 perhaps but little, above tide-level, the Wasatch was a low 

 Archaean range making part of the eastern limit of the Basin. 



2. In the shallow seas to the eastward, and beyond longitude 

 117£° W. westward, as explained by King, subsidence was still 

 continued ; and over the bottom, made of Carboniferous and 

 other older rocks (the Carboniferous of the Uinta area in- 

 cluded), Triassic and Jurassic beds were laid down. After- 

 ward on the east, Cretaceous deposition went forward over the 

 same area (but with probably somewhat contracted limits), the 

 subsidence still going on. 



3. The Triassic and Jurassic formations, compared with 

 those of other regions, are thin, and hence no unusual source 

 of sediment was needed for their accumulation and no great 

 height in the bordering lands ; but by the time the Cretaceous 

 period began, or during a post-Jurassic disturbance,* the dry 

 land had probably become more emerged and had received 

 some permanent additions. 



4. During the post- Cretaceous epoch of disturbance, the sedi- 

 mentary formations to the top of the Laramie were thrust 

 westward against the stable Archaean rocks of the Wasatch 

 Range, shoved up the Archaean slopes, forced into tortuous 

 flexures among the. Archaean peaks, and doubled up as they 

 were pushed through the gap. How much of the flexed 

 formations passed the summits cataclysmically into the Salt 

 Lake area of the time has passed out of record through denuda- 

 tion. 



* I refer for facts with regard to such a disturbance to the important paper 

 of Mr. S. F. Kmmons in the First volume of the Bulletin of the Geological Society 

 of America, " On Orographic Movements in the Rocky Mountains," p. 245. 



