282 THE AGE OF MAMMALS 



The Pacific Coast Region 



Before the Miocene epoch connection between the Atlantic and Pacific 

 oceans of Eocene times had wholly ceased, and the coast faunas of the 

 later Tertiary were wholly of the Pacific type. The Lower Miocene was 

 still a warm oceanic period; for we find in its fauna a nautilus still persist- 

 ing, and other genera now found only in southern waters. The accumula- 

 tion of organic remains along the Coast Range furnishes the series from 

 which the petroleum of. California was afterwards distilled. In the northern 

 interior vast outpourings of the Columbian lava flow (see p. 359) which 

 covered an area of more than 200,000 square miles, including the north- 

 eastern part of California, occurred about the middle of the Miocene. In 

 the Upper Miocene the climate of California was no longer sub-tropical, 

 but warm-temperate, and most like that of the states bordering the present 

 Gulf of Mexico. Marine animals like those of our time abounded in the 

 waters, and along with them were some southern forms. On the land, elms, 

 walnuts, hickories, and laurels flourished, indicating a temperate, rainy cli- 

 mate, more moist, if not more mild, than that of to-day in the same region. 

 In the Sierra Nevada Mountains of this epoch there were large rivers 

 winding slowly down low grades, overloaded with sediments, the auriferous 

 gravels, which spread out on low plains not far above sea level; through 

 subsequent elevation these flood-plain deposits are now found higher up on 

 the Sierra Nevadas, with their channels buried under later lava flows.^ 



Miocene Flora 



Our knowledge of the Miocene flora of North America is confined to 

 that of the ancient forests of the great mountain region, as described chiefly 

 by Knowlton " and Cockerell,^ extending from Colorado northward through 

 Montana, Nevada, Idaho, Oregon, and Washington. The famous 'Mas- 

 call' flora of Oregon is of Middle Miocene age; the similar but by no means 

 identical flora of Florissant, Colorado, is of somewhat more recent, per- 

 haps Upper Miocene, age. 



In the rich plant beds of the ancient lake deposits of all this region, 

 there is no record of the existence of any palms, although there are occa- 

 sional tropical plants and many warm temperate forms; yet the proportion 

 of tropical types is much smaller than in the Eocene. Sequoias are less 

 frequent. The horsetails (Equisetum) begin to be reduced both in num- 

 bers and size. The ginkgo still occurs, although it is less numerous. The 

 figs (Ficus) still flourish in Montana, Nevada, Idaho, and Oregon. This 

 gives us a hint as to temperature, for the fig now grows in northern Florida, 



' Smith, J. P., Salient Events in the Geologic History of California. Science, n.s.. 

 Vol. XXX, no. 767, 1909, pp. 346-351. 



2 See Knowlton, H. F., 1893, 1896, 1898, 1900, 1902, in Bibliography. 

 ' Cockcrell, T. D. A., 1906, 1908, in Bibliography. 



