344 THE AGE OF MAMMALS 



the beech (Fagus), the elm (Ulmus), which are all characteristic northerly- 

 types. We conclude that the Pliocene climate in this region was like tliat 

 of the Gulf of Mexico, or zone of the live oak, at the present time. It is 

 likely that the region of Chalk Bluffs, Nevada County, in Pliocene times 

 was sheltered by western ranges of mountains against the influence of 

 Pacific fogs; at all events, the absence of conifers seems to Indicate a 

 drier climate. A very striking feature of this flora is that which it 

 possesses in common with the Pliocene flora of central Europe, namely, 

 that it contains a large number of trees which no longer 

 grow on the Pacific slope of North America but are 

 now confined to the Atlantic slope. Among these are 

 species of the sweet gum (Liquidambar) , of the magnolia, of the prickly 

 ash (Zanthoxylum), and of the holly (Ilex). 



Some indication of the general age of this flora is found in the fact that 

 out of forty-two species, twelve are closely allied to Miocene types, while 

 thirty are more closely related to the present flora, especially of the Eastern 

 or Atlantic States. The conifers, including the sequoias, which are now the 

 most conspicuous element of the Sierras, did not exist, or at best were very- 

 rare, in Pliocene times in California (Lesquereux, 1882). 



The most recent contribution to the Pliocene flora of California is that 

 of Turner,' who records the following plants of Kirker Pass, California, 

 latitude 38°, as of Pliocene age: the date plum (Diospijros), the magnolia 

 (Magnolia), the laurel (Laurus), and the viburnum (Viburnum). The same 

 author notes that the flora from Corral Hollow, California (latitude 38°), 

 referred by Lesquereux to the Miocene, is, however, probably of Pliocene 

 age, as it is found associated with Pliocene shells. This flora includes horse- 

 tails (Equisetum), sequoias (Sequoia), yews (Taxites), alders, chestnuts, 

 willows, poplars, planes, laurels, cinnamons (Cinnamomum) , myrtles (Myr- 

 tus), red bays (Per sea), and sumac (Rhus). 



" Sirenians on the Pacific coast.^ — Other indications of mild climatic 

 conditions are found in the presence of mammals remotely allied to the 

 manatees and dugongs of the present equatorial belt. The remarkable 

 littoral or marine mammal known as Desmostylus derives its name from the 

 clusters of rounded and heavily enameled columns which constitute its 

 grinding teeth. The muzzle is slender and tapering, and armed with one 

 pair of incisors in the upper jaw and two pair in the lower. It is a large 

 animal, the skull being eighteen inches to two feet in length. According to 

 Merriam it is found only in marine formations of Pliocene age. It cer- 

 tainly inhabited both the eastern and western shores of the Pacific coast; 

 remains have been found in California, Oregon, and Japan. 



' Turner, H. W.. 1891. Geology of Mount Diablo. Bttll. Geol. Soc. Amer., Vol. II, 

 1891, pp. .396-397. 



- Marsh, O. C, Notice of a New Fossil Sirenian, from California. Amer. Jour. Sci., 

 Vol. XXXV, 1888, pp. 94-96. 



