532 FLORA OF Tin: i.auamik (;i;(trr. 



America, was purposely left out of the body of the table, for reasons 

 which have been stated. A column, however, was employed to record 

 the occurrence in that group of species belonging to any of the three 

 formations. A.n inspection of this column shows that 21 species are 

 common to the Laramie and the Green Eiver groups. Admitting this 

 to be Eocene, as well as the Mississippi Tertiaries, we have '26 species 

 common to the Laramie and American Eocene against 10 that are 

 common to the Laramie and European Eocine; this notwithstanding 

 that the American Eocene embraces less than a third as many species 

 as the European. 



We may carry this analysis further. There are 39 species common 

 and confined to the Laramie and the Miocene (inclusive of the Oligo- 

 cene). Of this number 21 are found in the American Miocene. Three 

 others occur in the arctic flora of Spitzbergen, Siberia, and other locali- 

 ties not in the western hemisphere, but the complete unity of the arctic 

 Miocene, and its almost total dissimilarity from the Miocene of Europe, 

 fairly warrant their addition to the American flora. Fifteen of these 

 are not found at all in the Miocene flora of Europe. This is surprising 

 when we consider how very small this combined North American and 

 arctic Miocene flora is compared with that of Europe. 



If we now divide the Laramie species that are also found in other 

 formations and localities into two classes, one of which shall embrace 

 all those occurring in American beds other than Laramie and the other 

 those occurring in no other American strata than those of the Lara- 

 mie, we shall have 55 such species out of a total of 80, 30 of which are 

 contined exclusively to the western hemisphere. The significance of 

 these figures, let me repeat, is greatly increased when we consider in 

 the same connection the magnitude of the European Tertiary flora, as 

 compared with that of America. 



We are thus brought once more face to face with the fact that while the 

 floras of Europe and America diftered widely in character during late 

 Cretaceous and Tertiary tnue, the beds of difterent age in each, respect- 

 ively, contained floras resembling each other to such an extent as to 

 warrant the conclusion that the later ones had descended from the 

 earlier without more than the natural amount of modification. When, 

 therefore, we coujAe these facts with those presented above as to the 

 relationships of the fossil to the living flora of the globe (where it ap- 

 peared that the American fossil flora resembles that of eastern North 

 America and southeastern Asia, while the European fossil flora re- 

 sembles that now found in Australia and the eastern half of the south- 

 ern hemisphere generally), we must conclude that some great disturb- 

 ing agencies have been at work since Miocene times which have caused 

 extensive migrations and profound alterations in the i)lant life of the 

 globe. It is no part of my purpose at present to discuss this jjroblem, 

 and I need scarcely say that it is to the influence of a series of great 

 fluctuations of temperature, causing glacial epochs, that these changes 



