THE MIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 283 



latitude 30°, and in Europe as far north as the Black Sea, latitude 40°, in 

 a January isotherm of 40° Fahr. to 50° Fahr. (4° C. to 10° C). In Oregon 

 is recorded Artocarpus, the breadfruit, now confined to the Pacific Islands. 

 Magnolias abound through all this region. We infer that in this moun- 

 tainous, volcanic, and well-forested region the climate was more equable, 

 and south temperate rather than tropical, with abundant moisture, but 

 not continuously humid. 



Predominant in the Miocene flora (Mascall) of the mountain region 

 were the following genera: 



Less abundant were the myrtles (Myrica), 

 Willows, Salix birches (Betula), alders (Alnus), laurels (Laurus), 



Poplars, Populus staff trees (Celastrus), maples (Acer), persimmons 



Sumach, Rhus (Diospyros), aralias (Aralia), ferns {Filices) and 



Walnuts, Juglans horsetails (Equisetum). 



Oaks, Quercus On the great plains and along the borders of 



Elms, Ulmus the great rivers which traversed them, the flora 



Plane trees, Platanus probably included types adapted to a warmer 

 Magnolias, Magnolia temperature. Of these we have' no direct knowl- 

 Figs, Ficus edge, as no plant beds are preserved. Certainly 



there is no proof of trqpical conditions north 

 of the fortieth parallel. 



As for the field flora of the plains an appeal must again be made to 

 the dental anatomy of the mammals, which demonstrates that grasses were 

 constantly increasing and formed the chief food of the prevailing types of 

 horses and ruminants in Upper Miocene times. 



Florissant Lake. — The deposits of the ancient lake basin of Florissant, 

 Colorado, now in the heart of the arid region of the Rocky Mountains, 

 elevated to a height of eight thousand feet, were especially monographed 

 by Samuel Hubbard Scudder,^ and more recently studied by T. D. A. 

 Cockerell,-' so that we now know the plants of its shores, the insects which 

 hovered about them, and other characteristics which are most significant 

 as to conditions in the border mountain region in Miocene times. The 

 lake lay in a long, narrow valley between granitic mountains, surrounded 

 by volcanoes, so that the very shales in which the remains of plants and 

 insects are entombed are wholly composed of volcanic sand and ash from 

 a source probably close at hand (Scudder, 1890, pp. 18-34). From con- 

 sideration of all the evidence, Cockerell ^ regards the age of these beds as 



' Scudder, S. H., The Tertiary Insects of North Ameriea. U.S. Gcol. Sun. Terr., Rept., 

 Vol. XIII, 1890. 



^ Cockerell, The Fossil Fauna and Flora of the Florissant (Colorado) Shales. Univ. Col. 

 Studies, Vol. Ill, no. 3, Boulder, Col., June, 1906; also. The Fossil Flora of Florissant, Col- 

 orado. Bull. Amer. Mus. Nat. Hist., Vol. XXIV, no. 4, 1908, pp. 71-110; and, The Miocene 

 Trees of the Rocky Mountains. Amer. Nalurnl., Vol. XLIV, no. 57, January, 1910, pp. 

 31-47. 



' Cockerell, letter to the author, March, 1908. 



