100 GEOLOGY. 



Thickness of the (Upper) Cretaceous system. — The maximum 

 thicknesses of the Cretaceous scries are something as follows: The 

 Laramie (including the Livingston), about 12,000 feet; t lie- Montana, 

 8700 feet; the Colorado, at least 3000 feet; the Dakota, about 300 

 feet. From these figures it will be seen that the Cretaceous system 

 is comparable in thickness to the systems of other periods. It should 

 be remembered, however, that these thicknesses represent maxima. 

 In the Black Hills, the Cretaceous has in some places a thickness of no 

 more than 1000 feet. In the Cinnabar Mountains (Montana), 4000 

 to 5000 feet; in the vicinity of Denver, about 13,000 feet; in Utah, 

 about 10,000 feet; in Kansas, 1000 to 1300 feet; in New Mexico, 3500 

 feet; in Manitoba, where the strata rest on the Devonian, 2000 feet, 

 and along the Northern Rockies in Canada, about 10,000 feet. 1 But 

 even these figures are much greater than those for most of the systems 

 of the Paleozoic periods, over the larger part of the area where they occur. 



The Pacific coast. 2 — On the Pacific coast, the Cretaceous system 

 is represented by the marine beds which constitute the Chico series, 

 which, at the time of its origin, probably extended along the coast 

 from Lower California to the Queen Charlotte Islands. The series is 

 found largely in great structural valleys, which were formed in pre- 

 Cretaceous times. 3 That part of the system w T hich has escaped erosion 

 has a thickness of 4000 feet in some parts of California. The Chico 

 series rests on the Shastan or Comanchean unconf ormably in the southern 

 part of the Coast Range of California, 4 and overlaps the Shastan 

 system at other points, resting on the Jurassic in the Sierras, and on 

 Paleozoic formations in southern California. 5 In some places the 

 Chico series rests on the Knoxville formation, the Horsetown formation 

 being absent. 6 Farther north, the Chico series sometimes rests on 

 the Shastan (Comanchean) system with apparent conformity, thus afford- 

 ing a local exception to the relation which generally subsists between 

 the two systems. In some parts of the Klamath Mountains, it rests 

 on schists of Devonian or greater age. In some parts of Oregon, the 



1 Am. Rept. Geol. Surv. Can., Vol. I. (N. S.), p. 69 B. 



2 See papers of Diller, Stanton, and Turner, cited under the Lower Cretaceous 

 (Shastan), p. 122. 



3 Anderson, Proc. Cal. Acad. Sci., Third Series, Vol. II, Pt. I. 

 Fairbanks, Jour, of Geol., Vol. Ill, p. 426. 



5 Fairbanks, Am. Jour, of Sci., Vol. XLV, 1893, p. 478. 



6 Anderson, op. cit. 



