228 GEOLOGY. 



to the different edible portions of the angiosperms. Grasses had 

 appeared in the Cretaceous and were present during this period. 

 Although the evidence is too scanty for positive affirmation, it is not 

 improbable that the shifting lakes and meandering rivers of the 

 Eocene gave rise to sedgy meadows and grassy plains, and through 

 these aided in the evolution of the grass-feeding herbivores and, as a 

 secondary consequence, led on to the evolution of the carnivores that 

 preyed upon them. It can scarcely be doubted that the sweet foliage 

 of the angiosperms proved a more congenial food for mammals than 

 the needles of the conifers, or the coriaceous and bitter foliage of the 

 pteridophytes. 



The Land Animals} 



The undifferentiated nature of the early Eocene placentals. — It is 



scarcely possible to carry our familiar conceptions of the mammalian 

 orders back to the Eocene prototypes, without importing distinctions 

 which did not then exist except as potentialities. The earliest Eocene 

 mammals were much more primitive and obscurely differentiated than 

 even those of the Middle Eocene, and this rapid backward convergence 



1 For the more important literature on the American Tertiary Mammalia, see the 

 numerous papers of Cope, Marsh, Osborn, Scott, Wortman, Matthew, and others, 

 particularly; Marsh: Introduction and Succession of Vertebrate Life in America, 

 Proc. A. A. A. S., Vol. XXVI, 1878, p. 211. The Origin of Mammals, Am. Jour. Sci. 

 Vol. VI, 1898, pp. 406-409, also Geol. Mag., Vol. VI, 1899, pp. 13-16. Cope: Ver- 

 tebrata of Tertiary Formations of the West, U. S. Geol. Surv., Vol. Ill, 1884. Osborn: 

 The Rise of Mammalia in North America, Am. Jour. Sci., Vol. XLVI, 1893, pp. 379- 

 392, and 448-466; the Evolution of the Teeth of Mammalia, Trans. N. Y. Acad. Sci., 

 Vol. XII, 1894, p. 187; the Origin of Mammalia, Rept. Brit. A. A. S., 1897, pp. 686- 

 687; also Am. Nat., Vols. XXXII and XXXIV, 1900, pp. 943-947, and Am. Jour. 

 Sci., Vol. VII, pp. 92-96, 1899, and many other papers. Scott, On the Osteology 

 of Mesohippus and Leptomeryx, with observations on the modes and factors of evo- 

 lution in the Mammalia, Am. Geol., Vol. IX, 1892, p. 428; Osteology and Relations 

 of Protoceras, Jour. Morph., 1895, pp. 303-374. Wortman: North American Origin 

 of the Edentates, Science, Vol. IV, 1896, pp. 865-866; the Ganodonta and their Rela- 

 tions to the Edentates, Bull. Am. Mus. Nat. Hist., Vol. IX, 1897, pp. 59-100; the 

 Extinct Camelidse of North America, Bull. Am. Mus. Nat. Hist., Vol. X, 1898, pp. 

 93-142. Matthew (W. D.), A Provisional Classification of the Fresh-water Tertiary 

 of the West, Bull. Am. Mus. Nat. Hist., Vol. XII, 1900, pp. 19-75; Ancestry of Cer- 

 tain Canidae, Viverridse, and Procyonidae. Adams (G. I.) : The Extinct Felidae of 

 North America, Am. Jour. Sci., Vol. I, 1896, pp. 419-444, and Vol. IV, 1897, pp. 

 145-149. 



