CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Part I. 



I. Introduction. 



The Cretaceous deposits of the Pacific Coast of North 

 America, as already known to geologists, lie within a narrow 

 continental border mainly to the west of the Great Basin 

 and the northern Cordillera. In their north and south 

 range the scattered and disconnected occurrences extend 

 from Mexico to Alaska and the Arctic Ocean, although they 

 do not territorially cover a large region. Represented upon 

 a map with other formations, they might hardly be noticed 

 except by one looking for them. They are but remnants, 

 or even mere traces, of what was once a more extensive 

 system of deposits, which in some places have been entirely 

 removed, and in others covered by later sediments, and in 

 some cases by volcanic flows. One of the largest and most 

 noteworthy of these remnants occupies the Sacramento 

 Valley in central-northern California, where it occurs in 

 unconnected dashes along its borders, in low hills flanking 

 the valley upon the east and west. 



Southward in California, the Cretaceous rocks are spar- 

 ingly distributed, occurring only at intervals in the Coast 

 Ranges, where they either form some of the lesser ridges or 

 protrude from beneath ridges of later sediments. In the 

 extreme southern portion of the State, and in Lower Cali- 

 fornia, they are confined to a narrow belt in the immediate 

 neighborhood of the coast, buttressed against the older 

 crystalline rocks of the interior. 



Northward in California, and in Southern Oregon, the 

 Cretaceous beds are restricted to the larger valleys lying 

 among the Klamath Mountains or upon their eastern out- 

 skirts; and here, also, they rest upon the older crystalline 

 or metamorphic rocks, and are overlaid by Tertiary or 

 Neocene deposits largely of fresh-water origin, or by 

 Neocene lavas. 



Within the boundaries of the Great Basin, the only 

 Cretaceous rocks that have been reported rest in a similar 

 manner upon a complex of early Mesozoic and older rocks. 



