INTRODUCTION 53 



and has aroused the interest of all mammaHan palaeontologists in turn, 

 including especially^ Cope (1879, 1884), Filhol (1885), Marsh (1891), 

 Scott (1888, 1889, 1894), and Osborn (1900, 1909). Especially interesting 

 historically are Cope's first comprehensive papers, "The Relations of the 

 Horizons of Extinct Vertebrata of Europe and North America" (1879),- 

 "The Horizontal Relations of the North American Tertiaries with those 

 of Europe" (1883),^ compared with Filhol's Critique of these papers (1885). 

 The most comprehensive recent paper is W. H. Ball's "A Table of the 

 North American Tertiary Horizons correlated with one another and with 

 those of Western Europe; with Annotations" (1898)/ Ball's attention 

 is especially directed to the southeastern portions of the United States, 

 particularly Florida, where an alternation of marine and fresh-water forma- 

 tions with vertebrate and invertebrate life zones affords a very direct 

 method of correlation with the European geological stages, which are nota- 

 bly distinguished by the alternation of marine and fresh-water conditions.'^ 



Geological Formations as a Record of Environments 



Our knowledge of what may be called the procession of environments 

 in different parts of the world during the Age of Mammals is derived from 

 three sources. First and foremost, from the structure of the animals 

 themselves, which fairly mirrors the habitat in which they lived; second, 

 from the impressions of plants which the rocks may contain; third, from 

 the nature of the rocks in which the fossil remains are found entombed. 

 These three kinds of evidence give us as complete a picture of the environ- 

 ment as we can ever hope to obtain, and they must be studied together. 

 They give us a vista of the succession of the meteorologic or climatic phases 

 of the period, of the general passage from warmer to cooler temperatures, 

 from moister to drier conditions. We are enabled to restore physiographic 

 conditions by separating the animals which naturally inhabit well-watered 

 forests, lowlands, and rivers from those naturally frequenting plains and 

 uplands, by separating those adapted to softer ground from those adapted 

 to dry, partially arid plains, and by adding to this information that de- 

 rived from evidences of successive fluviatile, flood plain, and aerial or seolian 

 deposits. Therefore the examination of the rocks in which mammals are 

 contained is little less important and interesting than the examination of 

 the fossils themselves; the two studies should go hand in hand. 



Beside the examination of the rocks another feature of geologic study 

 which dovetails with the pateontologic is the exact and precise record- 



' Principal titles are given in Bibliography. 



2 U.S. Geol. and Geog. Surv. Terr. Bull., Vol. V, no. 1, 1879. 



^ Cope, E. D., Section 2 of The Vertel)rata of the Tertiary Formations of the West, 

 Book I, 188.3, pp. 21-45. 



* U.S. Geol. Surv., 18th Ann. licpt., 1890-1897. 



5 See Dall, Geological Results of the Study of the Tertian,- Fauna of Florida, 1886-1903. 

 TraJis. Wagner Free Inst. Sci. Phila., Vol. Ill, Pt. 6, 1903, pp. 1541-1620. 



