GEOLOGIC RECORD OF CALIFORNIA 219 



Strata are most complete in the Coast Ranges. The Sierran record 

 is fragmentary, the formations being incomplete, separated by great 

 unconformities, including great masses of tuffs and igneous rocks, 

 and showing evidence of important recurring orogenic and volcanic 

 activity. 



The Coast Range province, too, showed this same phenomenon 

 in its Paleozoic and early Mesozoic sediments, but from the bottom 

 of the Cretaceous to the middle of the Miocene conditions were more 

 uniform, indicating moderately quiet advance and retreat of the sea, 

 with minor unconformities, smaller masses of igneous intrusives, 

 and outpourings of surface lavas. The Coast Range revolution, 

 about the middle of the Miocene epoch, broke the monotony of this 

 history, and for a time there was much mountain-making activity. 

 Minor outpourings of lava occurred along the coast, while farther 

 to the northeast the Columbian lava flood overwhelmed an area of 

 about two hundred thousand square miles, and the rejuvenation of 

 the Sierra Nevada was beginning. 



The Cretaceous section of the Coast Ranges is more complete than 

 that of any other single province in America. It lacks only the upper- 

 most portion, and shows a variety of conditions not seen anywhere 

 else, from the boreal faunas of the Knoxville to the tropical faunas 

 of the Horsetown and Chico epochs, with fossil floras interbedded 

 in every formation. 



The Tertiary marine section of the Coast Ranges is not only the 

 most complete in America, but also more complete than that of any 

 other single geographic region in the world. Every minor division 

 is fully represented by marine faunas, and most of them have fresh- 

 water beds intercalated, with fossil plants and freshwater animals. 



The Quaternary marine section of the Coast Ranges is the most 

 complete that has been described, for this is almost the only know^n 

 region where there has been much post-Quaternary orogenic activity. 

 In nearly all other regions the Quaternary sediments are still buried 

 under the oceans in which they were deposited. 



ROCK-FORMING AGENCIES OF CALIFORNIA 



Igneous rocks. — A large part of the surface of the state, a little 

 less than one-half, is made up of igneous rocks. Of these the most 



