﻿J. LeConte — Elevation of the Sierra Nevada. 17T 



the evidences of the age of the enlarged lakes as derived from 

 the vertebrate and the invertebrate remains in the lake deposits. 

 The latter are the same as those of L. Lahontan and are all 

 living now in rivers of California. The former are the mam- 

 moth, camels, gigantic edentates, horse, etc., and are referred by 

 Marsh to the Equus beds of the uppermost Pliocene. These 

 vertebrate remains are all on the surface and underlaid by the 

 recent shells, and Mr. Russell thinks they may have been 

 drifted in from older, i. e. Pliocene deposits ; for the testimony 

 of the invertebrates (shells) seems conclusive. But in any case 

 the mammoth, the gigantic edentates and the modern horse 

 are placed by nearly all authorities in the Quaternary. If we 

 reject Quaternary as a distinct period, and have only Tertiary 

 and Kecent, these animals may well be put in the uppermost 

 Pliocene instead of the Eecent. But if we are to have a 

 Quaternary or transition between the Tertiary and the Kecent, 

 then all these animals more properly belong to the Quaternary. 



Relation of the Post-Tertiary movement to the Great Lava-flood. 



The great Lava-flood of the Northwest, which covers an 

 area of 200,000 square miles, and where cut through by the Col- 

 umbia river, at the Cascade, is between 3,000 and 4,000 feet 

 thick, probably commenced to be outpoured at the beginning of 

 the Pliocene epoch. * The evidence of this is not entirely con- 

 clusive. All we know for certain is that it is immediately un- 

 derlaid by, and was therefore outpoured upon, eroded strata of 

 Miocene age. It is almost certainly, therefore, Post-miocene. 

 But the fact that great orographic movements over the whole 

 western half of the continent occurred at the end of the Mio- 

 cene (viz : the increased elevation of the Plateau region and the 

 cutting of the outer Grand Canon, and the letting down of the 

 Basin region on the one side and the Plains region on the other, 

 with the great increase of the size of the lakes in these regions ; 

 and especially the formation of the coast ranges of Pacific 

 coast), make3 it very probable that the great lava-flood was 

 associated with these movements and commenced at the same 

 time. But if so, it probably continued by successive fissure 

 eruptions through the whole Pliocene, and by volcanic erup- 

 tion almost to the present time. Certainly the great flows of 

 California were as late as the end of the Pliocene.f 



* "Great Lava-flood of the Northwest," etc., this Journal, vol. vii, p. It?,, 

 1874. Mr. Russell in his paper on Southern Oregon, p. 451, quotes me as refer- 

 ring the lava-flood to the Miocene. The underlying strata are Miocene. The lava 

 is probably Pliocene. 



f Mr. Ross Browne of the University of California, from very careful survey of 

 one of the old river beds of California finds evidence of several lava-flows, one 

 above another separated by gravels, but the greatest, and that which displaced 

 the river, was the latest. 



