THE COMANCHEAN PERIOD. 119 



The Northern Interior. 



Though the sea is not known to have had access to the western 

 interior of North America, north of Kansas, during the Comanchean 

 period, clastic beds of fluvial or lacustrine origin, which should per- 

 haps be referred to this period, are known at various points farther 

 north. The beds in question (sometimes classed as fresh-water Jurassic 

 under the names Morrison, 1 Como, 2 Atlantosaurus beds, etc.), occur 

 in parts of Wyoming, South Dakota (Fig. 349), Colorado, and New 

 Mexico, 3 though their distribution has not been accurately deter- 

 mined. 4 They probably reach northward to Montana, but they are 

 best known along the Front range through Colorado and Wyoming, 5 

 and in the Black Hills. 6 They extend south beneath the marine 

 Comanchean of southwestern Colorado, Oklahoma, and New Mexico. 7 

 Beds suspected of being of the same age are known in south- 

 western Wyoming and western Colorado. If these beds be the 

 equivalent of the Morrison, the formation is distributed, perhaps with 

 notable interruptions, over an area 600 miles long by 300 miles 

 wide (Fig. 379). The limited exposures are due to the fact that most 

 of the beds are covered by younger formations, being seen only where 

 there has been deformation and erosion. The rather remarkable uni- 

 formity of thickness of the formation, as thus far reported (commonly 

 between 200 feet and 300 feet), indicates that it was deposited on a 



1 Cross, Pikes Peak Folio, U. S. Geol. Surv., 1894. 



2 Scott, An Introduction to Geology, 1897. 



3 Lee, Jour, of Geol. Vol. X, pp. 36-50. 



4 The following references touch the question of the classification of these beds: 

 Marsh, O. C, Proc. Amer. Assoc. Adv. Sci., 1878, Vol. XXVI, pp. 210, 220; Amer. 

 Jour. Sci., ser. 4, 1896, Vol. II, pp. 433-47; Amer. Jour. Sci., ser. 4, Vol. VI, 1898, 

 pp. 105-15; Osborn, H. F., Jour. Acad. Nat. Sci. Phil., 1888, Vol. IX, p. 187, and 

 Scott, W. B., Introduction to Geology, 1897, p. 477; Knight, W. C, Bull. Geol. Soc. 

 Amer., 1900, Vol. XI, pp, 383-87, and Wyo. Exp. Sta. Bull. 45, p. 138; Ward, Les- 

 ter F., 20th Ann. Rept. U. S. G. S., 1900, Pt. II, p. 377; Williston, S. W., Amer. Jour. 

 Sci., ser. 4, 1901, Vol. XI, p. 114, and Jour, of Geol., Vol. XIII, 1905, p. 338; Hatcher, 

 J. B., 1903, Memoirs Carnegie Mus., Vol. II, No. I, pp. 67-72; Darton, N. H., Bull. 

 Geol. Soc. Amer., 1904, Vol. XV, pp. 388, 425, and Edgemont and New Castle folios, 

 U. S. Geol. Surv. 



5 Knight classes the Como beds with the Jurassic. Bull. 45, Wyo. Exp. Station, 

 p. 134. 



6 Ward, Jour. Geol., Vol. II, p 250. 



7 Stanton, Jour. Geol., Vol. XIII. The latest studies, reported in this paper, leave 

 the age of this formation in doubt. 



