Dahe — Episodes in Rocky Mountain Orogeny. 245 



Aet. XV. — Episodes in Rocky Mountain Orogeny; by C. 

 L. Dake, Missouri School of Mines. 



In a recent article in the Journal of Geology, Dr. Cham- 

 berlin calls attention to the dual nature of the Rocky 

 Mountain or Laramide revolution,^ in which ^ ' at least two 

 distinct periods of folding have been distinguished. ' ' He 

 also notes that similar conditions obtain in southwestern 

 Wyoming. The present writer is in possession of con- 

 firmatory evidence, from northwestern Wyoming, show- 

 ing distinctly more than one episode of disastrophism in 

 the locality between Cody and Yellowstone Park. The 

 facts upon which this statement is based have in part 

 been presented by the writer in a previous paper.- The 

 facts already made public, together with those not hereto- 

 fore published, may be briefly summed up as follows. 



In Sec. 21, T. 52 N., R. 104 W., south of Morris Post 

 Office, occur nearly flat-lying outcrops of pebbly sand- 

 stone interbedded with red and gray shales, provisionally 

 assigned to the Fort Union (?) as that term is used by 

 Hewett, in the Shoshone River Section.^ The pebbles in 

 these beds are abundant and average one-fourth to one- 

 half inch in diameter but reach a maximum of over two 

 inches. They are well rounded and include red granite, 

 basalt, brown quartzite, sandstone, black chert, brown 

 chert, and shale. The red granite is wholly similar to 

 that found in the pre-Cambrian of the region, and the 

 cherts can be duplicated in the Carboniferous rocks. No 

 granites are kno^vn in this locality younger than pre-Cam- 

 brian, and no source for the cherts more recent than the 

 Embar (Pennsylvanian). The quartzite is comparable to 

 the Quadrant (Tensleep) quartzite (Pennsylvanian) ex- 

 posed fifteen or twenty miles north of here. Hewett,^ in 

 the Shoshone River Section, found cherts with Pennsyl- 

 vanian faunas in apparently equivalent beds of Fort 

 Union age ; also pebbles of pink granite in the same beds. 

 The pebbly sandstone rests on beds of Cody (Colorado- 

 Montana) age, and the presence of pebbles of pre-Cam- 



^ Chamberlin, EoUin T. ; The Building of tlie Colorado Eockies, Jour. 

 Geol., XXVII (1919), pp. 151-164 and 225-251. 



^ ' ' The Hart Mountain Overthrust and Associated Structures in Park 

 County, Wyoming," Jour. Geol., 26, pp. 45-55, 1918. 



^ Hewett, D. F. ; The Shoshone River Section, TJ. S. Geol. Survey, Bulletin 

 541, pp. 89-113. 



* Hewett, op. cit., p. 105. 



