PALEOBOTANICAL EVIDENCE 535 



seems a safe assumption that the climate was at least temperate. It is 

 important to note that a considerable number of unmistakable harbaceous 

 types were present. 



There is a small Upper Miocene flora found at Elko, Xevada, that is 

 apparently of the same age as the Florissant lake beds, but it is too small 

 to be of much value in the present connection. In approximately the 

 same position is a small florule of 14 species from Esmeralda County, 

 Xevada. It indicates a higher degree of moisture than at present obtain- 

 ing and altogether a climate probably like that of the Southern States. 

 In California the auriferous gravels have yielded a flora of some 125 

 species, many of them of very modern appearance, such as Acer, Arto- 

 carpiis. Magnolia, Persea, Quercus, Castanopsis, Zizyphus, etcetera. On 

 account of their obvious affinity with the living flora, they were at first 

 referred to the Pliocene by Lesquereux, but later they came to be re- 

 garded as Middle Miocene. This flora is much in need of critical 

 revision, and latest stratigraphic studies seem to indicate that the 

 auriferous gravel phase may possibly have begun in the uppermost 

 Eocene and continued on well into the Miocene. In the John Day 

 Basin of Oregon there is the Middle Miocene Mascall flora of about 80 

 forms. It includes Sequoia, Glyptostrobus, Taxodium, Populus, Salix, 

 Juglans, Hicoria, Quercus, Ulmus, Planera, Magnolia, Laurus, Platanus, 

 Ehus, Acer, Sapindus, etcetera, and altogether indicates at least a tem- 

 perate climate. In the Yellowstone Xational Park there are two small 

 Miocene floras that have much the same facies as that last considered and 

 point to much the same conclusion regarding its climatic indications. 

 The numerous fossil trees so prominent in the park all show strongly 

 defined growth rings. To the north, in the Canadian provinces, Dawson 

 has signalized the Upper Miocene flora of the Similkameen Valley, a 

 flora of some 25 forms, all indicating temperate conditions. 



In the Old World many and widely scattered Miocene floras have been 

 made known, tlie most extensive and most completely exploited being 

 that of Switzerland, as described by Oswald Heer.^^ This flora includes 

 some 920 species, of which number 114 are so-called floAverless plants and 

 806 are flowering plants. Of the latter, 291 are species of trees and 242 

 are shrubs, or 533 species of woody plants. The herbaceous flowering 

 plants number 1G4 species. On the basis of certain proportions between 

 the several groups of plants, Heer concludes that the full Miocene flora 

 of Switzerland could hardly have been less than 3,000 species, which is 

 far in excess of the number now living there. Associated with the plants 



21 Oswald Heer : Flora Tertiaria Helvetia^, vol. 1, 1854 ; vol. 2, 1856 ; vol. 3, 1859. 

 XXXVII — Bull. Geol. Soc. Am., Vol. 30, 1918 



