818 HISTORICAL GEOLOGY. 



over Mexico during this time the Athxntic and Pacific oceans were united. 

 He makes the thickness 20,000 feet. 



Rocky Mountain region and Central Interior. — The Lower Cretaceous of 

 the Eocky Mountain region includes, at some localities at base, the fresh-water 

 Kootanie beds of Dawson (1885), so named from the Kootanie Pass, in the 

 Kocky Mountains, about 30 miles north of the 49th parallel, where they were 

 first found and characterized by their fossil plants. The beds are sandstones 

 and shales, and contain some coal. Other localities occur at intervals to the 

 northward for 150 miles, and to the southward in western Montana. The 

 beds also outcrop, according to recent determinations by L. F. Ward, about 

 the Black Hills, in western Dakota, where they have a thickness of 200 to 

 300 feet, contain trunks of Cycads and other plants, and underlie plant beds 

 of the Dakota group (Upper Cretaceous) to which they had been referred. 

 How far they extend eastward and southward is not yet ascertained. In 

 New Mexico they are mainly marine beds, and resemble those of Texas, with 

 which they are continuous. 



Pacific harder. — The Lower Cretaceous beds of the Pacific border in the 

 United States are marine, but in British Columbia they are partly of fresh- 

 water or marsh origin. They occur (1) in the Plateau or interior region of 

 British America, and (2) along the Coast belt. 



Over the Plateau region they are described as extending over Washington 

 to the Yukon district and northward to the Arctic Ocean (G. M. Dawson). 

 The Plateau region within the United States, that is, the Great Basin, was 

 apparently emerged ; but south in Mexico, as already described, long sub- 

 mergence is proved by the existence of many thousand feet in thickness of 

 Lower Cretaceous beds. 



The coast region has a border of Lower Cretaceous beds along the greater 

 part of California and Oregon, and also on Queen Charlotte Islands and 

 Vancouver Island ; and again far north along both the northern and southern 

 shores of the Alaskan peninsula. 



The beds in California constitute the Shasta group of J. D. Whitney 

 (1869). They are well exposed along the western border of the Sacramento 

 valley, where they are divided into the Knoxville and Horsetown beds — 

 so named from localities in the region by C. A. White. These two groups 

 were made by White to represent only part of the Shasta group ; but later 

 observations by Diller and Stanton (1893) show that they correspond to 

 the whole. In Tehama County the total thickness is about 26,000 feet ; in 

 Shasta County, where the Horsetown beds alone occur, 5200 feet (Diller, 

 Stanley-Brown). The Knoxville or lower group has among its fossils various 

 forms of Aucellce (Pigs. 1203-1205, page 759), and the Horsetown includes 

 in its abundant fauna many Ammonites ; the species of the two have close 

 relations to the Neocomian, Gault, and intermediate beds of Europe. The 

 two groups in California thus cover the whole of the Lower Cretaceous ; and 

 these are continued in the Chico series of the Upper Cretaceous (Diller). 



In British America, the lower part only of the coast Cretaceous on Van- 



