300 ANNUAL OF SCIENTIFIC DISCOVERY. 



down from the mountain hights above and deposited in pre-existing 

 valleys : sometimes in very narrow accumulations, simple beds of 

 ancient rivers, and at other times in wide lake-like expansions of for- 

 mer watercourses ; and this under the action of causes similar to those 

 now existing, but probably of considerably greater intensity. The 

 deposition of detritus, for the most part auriferous, took place during 

 the later Pliocene epoch, and not as late as the drift or diluvial period, 

 as is abundantly proved by the character of the remains of plants and 

 land animals which are imbedded in it. The deposition of this aurif- 

 erous detritus was succeeded, throughout the whole extent of the 

 Sierra Nevada, by a tremendous outbreak of volcanic energy, during 

 which the auriferous gravel was covered by heavy accumulations of 

 volcanic sediments, ashes, pumice, and the like, finally winding up by 

 a general outpouring of lava, which naturally flowed from the summits 

 of the Sierra through the valleys, into the lake-like expansions, filling 

 them up and covering over the auriferous gravels, which were to re- 

 main for ages, as it were, in a hidden treasure-chamber, concealed 

 under hundreds of feet in thickness of an almost indestructible ma- 

 terial. 



The effect of the denudation which has taken place since these 

 streams of lava flowed down the mountains, has been most extraordi- 

 nary. For now, these deposits of gravel and overlying volcanic 

 materials, instead of occupying the depressions of the surface, are 

 found forming high plateaux between the present river canons and 

 flat-topped ridges, known as " Table mountains," hundreds or even 

 thousands of feet above the present river beds. Thus the topography 

 of the country is exactly the reverse of what it was at the commence- 

 ment of the present geological epoch : what were once valleys arc 

 now ridges, and the ridges of former times were where the im- 

 mense canons of the rivers flowing 'down the western slope of the 

 Sierra now are. 



The Mammalian remains found in the tunnel and placer diggings of 

 California seem to belong to two distinct epochs. The oldest repre- 

 sents the Pliocene, the other the Post-tertiary. The former are found 

 under the volcanic beds, the latter in de-posits which have been formed 

 since the period of greatest volcanic activity, and which apparently 

 belong to the epoch of Man. For it appears that the facts collected 

 by this Survey, when fully laid before the public, will justify the asser- 

 tion flint the m-istodon and ei-'}>!t>n>! , ir/tose remains are so widely and 

 aim n<l < i n1 1 u scattered through California, have been cotemporaneous 

 with M'iit in that reyion. 



The Highest Mitn!<iins in the Untied tilafes. A reconnoissance of 

 tin- Sierrarange, between the parallels of 3ii and 38, recently under- 

 taken by Messrs. Brewer, King, and others, shows that this portion 

 of the State of California, previously unexplored and unknown, contains 

 the greatest mass of mountains, taking width and average elevation 

 into consideration, which has yet been discovered within the limits of 

 the United States, and perhaps on the North American Continent; at 

 one point, within the field of view of the explorers, there were observed 

 five mountains of over 14,000 feet elevation ; and about 50 peaks 

 which ruse to a hight of over 13,000 feet. The culminating point 

 of the Sierra Nevada in this district was, moreover, believed to be not 



