INTRODUCTION 51 



Palosontologie (1876-1893). Full and more precise lists of the European 

 mammals characteristic of different formations or horizons are those as- 

 sembled by Schlosser (1887-1890). The Literal urbericht (1883-1897) 

 of the same author, a complete review of the literature of mammalian 

 palaeontology for the fourteen years indicated, is a mine of wealth for an 

 investigation of this kind. Up to 1896, however, there still existed no 

 satisfactory correlation of all the Old World horizons with each other, and 

 it was obvious that a unified Old World system was absolutely necessary 

 as a starting-point for exact comparison with the formations of the New 

 Workl. Kealizing that an acceptable working basis could only be secured 

 by cooperation, Osborn drew up in 1897 a Trial Sheet of the Typical and 

 Homotaxial Tertiary Horizons of Europe and circulated it for criticism and 

 suggestion. Invaluable corrections were received, especially from the 

 author's friends Gaudry, Von Zittel, Schlosser, Pavlow, Boule, Lydekker, 

 and Deperet. The corrections were embodied in a Second Trial Sheet 

 (April 15, 1898), which was used for further personal investigation and dis- 

 cussion with the above-named palaeontologists, also with Lepsius of Darm- 

 stadt and Forsyth Major of the British Museum. A Third Trial Sheet, 

 issued in 1900, was more accurate than its predecessors, but still lacked 

 the desired exactness and fullness. The general state of knowledge in 1900 

 was brought together in the author's paper, ''Correlation between Tertiary 

 Mammal Horizons of Europe and America." ' In June, 1905, there began 

 in the Comptes Rendus de V Academic des Sciences the epochal series of 

 papers by Deperet entitled U evolution des Mammi feres tertiaires ; im- 

 portance des 7ni(jrations. These papers covered with the desired fullness 

 and precision the sul)ject of the correlation of all the mammal-bearing 

 formations of Europe, and moreover treated briefly and with great preci- 

 sion the succession of mammalian life in Europe, and the supposed migra- 

 tions between the continents of the main land masses of Europe, Asia, 

 Africa, and North America. Deperet 's life zones and faunistic subdivisions 

 of the Old World are adopted throughout the present volume as the stand- 

 ard for comparison with the New World. His correlation of formations 

 is graphically expressed in a full series of maps. (See Figs. 26, 50, etc.) 



American Correlation. — The chronological correlation of American 

 mammal-bearing formations with each other opened in a very promising 

 way through the exact methods which characterized even the early ob- 

 servations of the geologist Hayden and the pahBontologist Leidy on the 

 geologic formations of our Great Plains. Naturally errors cYo\)i into such 

 a rich and new field, where many formations were so similar to (>ach other 

 in external appearance, and in a period of geologic thought which jirecetled 



' Osborn, H. F., Correlation between Tertiary Mammal Horizons of Europe and Amer- 

 ica; An Introduction to the more Exact Investigation of Tertiary Zoogeography; Prelimi- 

 nary Study with Third Trial Sheet. Ann. New York Acad. Sci., Vol. XIII, no. 1, July 21, 

 1900, pp. 1-64; and, Correlation des horizons de mammifc^rcs tertiaires en Europe et en 

 Amerique. C. R. 8" Cong. geol. intern., 1900, pp. 357-363. 



