PALEOGEOGRAPHY OF THE MESOZOIC 513 



black area in figure 6 ) . At the close of the Jurassic, however, the Sierra 

 Nevada folds were thrown up to the southeast of this arch, and it was 

 then incorporated into the area of the Sierra Nevada Disturbance. We 

 have seen that this late Jurassic movement also forever shut out the 

 former wide extension of the Pacific, not only from the area of the 

 United States, but from most of western North America as well. 



When we study the paleogeography of Cretaceous time, it soon becomes 

 apparent that the conditions of oceanic spreading had been further 

 altered toward the close of Shastan time, for subsequent to this period 

 the Pacific overlaps were narrow (oblique lines to left in figure 6), and 

 over what is now the site of the Rocky Mountains, and far to the east in 

 both Canada and the United States, a new inland sea appeared — the 

 Coloradoan Sea of Cretaceous time — extending from the Gulf of Mexico 

 into the Arctic Ocean (oblique lines to right in figure 6). The barrier 

 that kept these waters apart was the newly bowed-up land to the west of 

 the present Eocky Mountains, the Cordilleran Intermontane Belt of 

 Ransome, and this barrier continued to rise throughout all of Cretaceous 

 and much of Tertiary time (horizontal lines in figure 6). We see here, 

 therefore, the beginning of the process which made the Cordilleran Inter- 

 montane Belt of elevated plateaus, extending from Arctic Alaska all the 

 way into Central America, and it is for this reason that the movement 

 may be called the Cordilleran Intermontane Disturbance. Blackwelder 

 has recently named it the Oregonian deformation, but this term is of 

 altogether too local significance. 



CRETACEOUS OB CHICO TIME 



(See Figure 7) 



The Chico series of sandstones and shales, with local conglomerates 

 and coal beds, usually overlies the Shastan formations unconformably. 

 These coarse deposits and thick formations are found all the way from 

 the Lower Yukon, the Alaskan peninsula (1,000 feet thick), Queen 

 Charlotte (11,000 feet) and Vancouver (5,000 feet) islands, middle and 

 southern Oregon (1,000 feet), the Sacramento Valley (9,500 feet), and 

 the Coast Eange of California, to San Diego and the peninsula of Lower 

 California. Stanton states that the Chico series begins somewhat earlier 

 in time and continues longer than the Colorado series of the great In- 

 terior Sea, but does not embrace strata of youngest Cretaceous time. 

 The Chico faunas are of the Indo-Pacific province and are markedly dif- 

 ferent from those of the Coloradoan and Mexican seas. The two prov- 

 inces were separated from one another by the rising Rocky Mountain 

 barrier. 



