Geology. 89 



the rivers are comparatively modern. In the mountains from the 

 Basal Eocene to the John L)ay the rocks are not worked over, as 

 erosion was retarded by the heavy cappings of lava in the John 

 Day basin of Oregon, in the Bridger basin by a dense Pleistocene 

 (?) conglomerate and in the Washakie by a fine conglomerate. 



In the plains region, by contrast, the very extensive Oligocene 

 strata were in part worked over to form the Miocene and these in 

 turn to form the Pliocene ; all three contributed to the Pleis- 

 tocene, and all four are now contributing to the alluvium of the 

 Great Plains. 



The successive faunal phases are : — ; 



1, Archaic Mesozoic mammals with partly South American, 

 partly European affinities. Basal Eocene. 



2, The first modernization, invasion of the archaic by the 

 modern fauna — whence is not surely known, but Osborn favors a 

 North American-Asiatic or Holarctic origin ; the severance of the 

 South American land connection — Initial elimination of the 

 archaic fauna in competition with the modern. Wasatch. 



3, Absence of fresh Eurasiatic migration, descendants of archaic 

 and modern mammals slowly evolving and competing, with the 

 gradual elimination of the archaic. Establishment of the North 

 American Artiodactyla. Wind River to close of Mocene. 



4, Second modernization — First knowledge of the plains' fauna 

 — Absence of all archaic mammalia except the Ltyaenodontidse — 

 Peestablishment of faunal resemblances with western Europe. 

 Oligocene aud Lower Miocene. 



5, Fresh migrations from Europe. First proboscidians and 

 true Felinse. Middle Miocene to Lower Pliocene. 



6, Land connection with South America. Intermigration of 

 North and South American mammals. Middle and Upper 

 Pliocene. 



7 Increasing cold, moisture and forestation. Third moderniza- 

 tion by Eurasiatic invasion— Gradual extinction of larger 

 Ungulata. Pleistocene. 



Conclusion : — North America promises to give us a nearly 

 complete and unbroken history of the Tertiary in certain regions, 

 which are, after all, comparative^ restricted. Middle and ITpper 

 Eocene are approaching solution ; Lower and Basal Eocene still 

 require additional surveys. The chief remaining gap is now in 

 the Pliocene stratigraphy, materials being at hand for an estab- 

 lishment of the Pleistocene sequence. r. s. l. 



8. New Fossil Mammals from the FayiXm Oligocene, Egypt ; 

 by Henry Fairfield Osborn. Bull. Amer. Mus. Nat. Hist., 

 vol. xxiv, 1908, pp. 265-272, with 6 text figures. 



New Carnivorous Mammals from the FayiXm Oligocene, 

 Egypt ; by H. F. Osborn. Ibid., vol. xxvi, 1909, pp. 415-424. 

 and 9 text figures. — In these two papers Professor Osborn 

 describes part of the remarkable wealth of material collected in the 

 Fayum by the expedition from the American Museum sent out 

 during the winter of 1906-1907. The first paper contains descrip- 



