CEETACEOUS PERIOD. 453 



Jurassic rocks enter into its constitution (their fossils being found along 

 a distance of 250 miles, on the western side), while the Cretaceous 

 beds lie unconformable on the flanks of the mountains. The chain, 

 in the language of Professor Brewer (in a review of Whitney's Geo- 

 logical Report), " consists essentially of an immense core of granite, 

 flanked on either side by metamorphic slates ; " " the culminating 

 points in the southern portion [Mt. Whitney, the highest among them, 

 about 15,000 feet above the sea] are of granite ; in the central, of 

 slates ; and in the northern, of volcanic rocks " [of later date]. Yo- 

 semite Valley lies in the broad central granite belt of the southern 

 part. Again he says, " In passing along the foot-hills of the chain, at 

 its western base, we find, at numerous points, the marine Tertiary, or 

 Cretaceous, or both, resting in a horizontal position on the upturned 

 edges of the metamorphic rocks of the auriferous series." " These 

 horizontal strata occur at intervals for over 400 miles, along the west- 

 ern base of the chain ; " " to the north, the Cretaceous predominating, 

 and to the south, the Tertiary." 



As the quartz veins intersect the Triassic and Jurassic (now meta- 

 morphic) slates, they also are part of the results of the great upturn 

 and uplift. They show where the leaves of the slates were opened or 

 broken, and where great fractures were made through the deep forma- 

 tions, in the course of the upturning ; and where the heat, developed 

 by the upturning, turned all water or moisture present into hot alka- 

 line solutions of silica ; and these solutions, passing into the cavities 

 and all opened spaces, deposited the silica and so filled them with 

 quartz. Thus the auriferous quartz " reefs " or veins were made ; for 

 the gold and all associated metallic ores were carried in at the same 

 time, the hot waters gathering them far and wide from the slates ad- 

 joining. Some of the auriferous quartz veins thus made are of extraor- 

 dinary size. " In the Pine Tree and Josephine mines, near the north 

 end of the [Mariposa] estate, the average breadth of the quartz is 

 fully twelve feet ; and in places it expands to forty feet." 



While the Sierra Nevada was in jjrocess of formation on the east- 

 ern borders of California, the Wahsatch, another high range parallel 

 with it, and the Uintah, a transverse range, were in progress, accord- 

 ing to the observations of Clarence King, over a region east of the 

 meridian of Great Salt Lake ; and still others, called the Humboldt 

 ranges, over the plateau between the Sierra and the Wahsatch. 



3. CRETACEOUS PERIOD (18). 



The Cretaceous period is the closing era of the Reptilian Age. It 

 is remarkable for the number of genera of Mollusks and Reptiles 



