122 GEOLOGY. 



taceous strata are not known. They may underlie some parts of the 

 later formations between these localities, or they may be wholly absent. 



The Pacific Border. 



In the United States. — The Lower Cretaceous beds have great 

 development in California, where they attain their maximum known 

 thickness. They here constitute the Shastan group, 1 made up of two 

 principal divisions, the Knoxville below, and the Horsetown above. 

 The former has a maximum thickness of about 20,000 feet (according 

 to estimate), and the latter of 6000 feet. These thicknesses are local 

 and exceptional, but thicknesses of 12,000 to 15,000 feet have been 

 calculated in several places. The Sacramento valley was the site 

 of the thickest deposits, the sediments being furnished by the newly 

 uplifted Sierra and Coast ranges. Throughout most of the great 

 series, including the basal beds, there are evidences of shallow-water 

 origin. 2 Dark clay slates predominate, but there is also a nota- 

 ble amount of sandstone. The fossils of the Knoxville beds, like those 

 of the Jurassic of the same region, point to faunal connections with 

 Russia, while those of the Horsetown beds seem rather to point to 

 connections with southern Asia and Europe. These changes in life 

 imply geographic changes of importance. 



The Shastan group is found along the western side of the Sacra- 

 mento valley, and in the Coast ranges of California, Oregon, 3 and Wash- 

 ington. Where its base has been observed, it sometimes rests on 

 metamorphic rocks of unknown age, and sometimes on the Jurassic. 

 It is overlain unconformably 4 in some places, and without apparent 

 unconformity in others, by the Upper Cretaceous (Chico 5 ), while in 



1 Gabb and Whitney, Paleontology of Cal., II; White, On the Mesozoic and 

 Cenozoic Paleontology of California, Bull. 15, U. S. Geol. Surv. ; Becker, Bull. 

 19, U. S. Geol. Surv.; Turner, Geology of Mount Diablo, Cal., Bull. Geol. Soc. Am., 

 Vol. II; Diller, Cretaceous Rocks of Northern California, Am. Jour. Sci., Vol. XL, 

 1890, and Cretaceous and Early Tertiary of Northern California and Oregon, Bull. 

 Geol. Soc. Am., Vol. IV, 1892; Diller and Stanton, idem, Vol. V, The Shasta-Chico 

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



2 Diller and Stanton, Bull. Geol. Soc. Am., Vol. V. 

 3 Merriam, Jour, of Geol., Vol. IX, 1901, p. 71. 



4 Becker, Bull. 19, U. S. Geol. Surv., p. 12; also Monograph XIII, U. S. Geol. Surv , 

 p. 188. 



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

 Geol. Surv. 



