THE COMANCHEAN PERIOD 733 



nay and Cascade formations, 1 etc.) similar in character to those just 

 mentioned. They are mainly clastic, and contain some coal. Their 

 fossils are mostly of plants of early Cretaceous types. In Montana, 

 the Kootenay formation overlies the Morrison. The exact relations 

 of these formations to the Comanchean of the Atlantic and Gulf 

 coasts is not known. 



To the Morrison and Kootenay formations a lacustrine origin 

 has usually been assigned, and there is perhaps no adequate ground 

 for questioning this conclusion for some parts of the formations; 

 but the character of some of the beds and the nature and distribu- 

 tion of their fossils suggest a fluviatile origin for parts, and perhaps 

 for large parts, of the series. The position of these formations with 

 reference to the Rocky Mountain axis, is much the same as that of 

 the Potomac series to the Appalachian axis, and a similar conception 

 as to the mode of origin may be entertained. 



The Pacific Border 



In the United States. The Lower Cretaceous beds have great 

 development in California, where they attain their maximum 

 known thickness. They are known here as the Shastan group, 2 

 made up of the Knoxville series below and the Horsetown above. 

 The deposits are thickest in the Sacramento valley, the sediments 

 having been furnished by the newly uplifted mountains (p. 710). 

 Most of the thick system, including its basal beds, bears the marks 

 of a shallow-water origin. The Shastan group is represented in 

 Oregon also. 3 



Where the base of the Shastan series has been observed, it is 

 unconformable on Jurassic rocks, or on metamorphic rocks of un- 

 known age. It is overlain unconformably in some places, and with- 

 out apparent unconformity in others, by the (Upper) Cretaceous 

 (Chico 4 series) . In the Coast Range of California, the system 

 contains some igneous rock. 



1 Fort Benton, Mont, folio, U. S. Geol. Surv. 



2 Turner, Bull. Geol. Soc. Am., Vol. II; Diller, Am. Jour. ScL, Vol. XL, 

 1890, and Bull. Geol. Soc. Am., Vol. IV, 1892; Diller and Stanton, idem, Vol. 

 V, a Summary for the Pacific Coast brought up to 1894. 



3 Diller, Am. Jour. Sci., Vol. XXIII, 1907. 



"Fairbanks, Jour. Geol., Vol. Ill, pp. 415-430, and San Luis, Cal., folio, 

 U. S. Geol. Surv. 



