A UR I FERGUS GRA VELS— INDEPENDENCE HILL FLORA 893 



period is scant and no positive conclusions as to age can be 

 drawn from it, it must be conceded that it is very closely allied 

 to that of the bench gravels. While more extensive collections 

 might show it to be of Pliocene age, yet the characteristic forms 

 contained in it prove that up to the beginning of the rapidly 

 succeeding andcsitic flows there was no great change of clhmate. 



Age of the andcsitic flozvs. — Mr. Turner has at various points 

 found fossil wood in the andcsitic tuffs (Alpine county, eleva- 

 tion 7000 feet) which Professor Knowlton has identified as conif- 

 erous and designated as Ctcpressitioxylon and Pityoxyloti.^ No 

 trees referable to the former genus occur at this elevation at the 

 present time, from which it may be inferred that the climate 

 during the andcsitic period was milder than now. 



To recapitulate, the deep gravels are probably of Eocene or 

 Lower Miocene Age, the bench gravels and the rhyolitic tuffs 

 are with considerable certainty of Miocene, probably Upper 

 Miocene Age. The age of the gravels of the inter-volcanic 

 erosion period and of the andcsitic tuff is not established beyond 

 doubt, but probably belongs to the lower Pliocene or Upper 

 Miocene. The eroded surface upon which the auriferous 

 gravels were deposited was consequently produced either during 

 the earliest Miocene or during the Eocene. 



It is of interest to note that Professor Knowlton in his 

 extended studies of the floras of the Yellowstone National 

 Park,^ has found a flora which he calls the Lamar flora and refers 

 to the Upper Miocene ; this flora he states bears a very close 

 resemblance to that of the auriferous gravels. 



REVIEW OF THE POST-JURASSIC HISTORY OF THE SIERRA NEVADA. 3 



In the following lines a short summary is given of the diffei- 

 ent phases of the history of the Sierra Nevada between the 



'Am. Geologist, Vol. XV, June 1895, p. 375. 



* Arnold Hague, The Age of the Igneous Rocks of the Yellowstone National 

 Park, Am. Jour. Sci., June 1896, p. 452. 



3 Unless otherwise stated, the results in this paper have only reference to the 

 belt here studied. Many of them will be applicable to the whole range, but this needs 

 confirmatory study. 



