CHAPTER III. 



Sources op the Vegetation: ^Migrations. 



PRACTICALLY all of the northern Rocky Mountain re- 

 gion and plains have been glaciated and the subsequent 

 plant covering derived from outside areas in later times 

 (24). The sources from which these migrations have ensued were 

 several, including chiefly Atlantic and Pacific elements as indi- 

 cated by the existing species. A southern element likewise enters 

 to some extent, but is important only here and there locally, so 

 far as the woody species are concerned. 



That any relation exists between the species at present 

 growing in this region and those antedating the glacial period 

 is neither impossible nor improbable, but is difficult of proof. 

 Of the many (50) genera of woody angiosperms listed below, 

 mostly from the strata of the Tertiary of this immediate region. 

 nearly all are represented by one or more species within the 

 temperate latitudes of North America, and the majority of the 

 existing genera of like sort in ^Montana are represented in the 

 fossils of that period. Of the Tertiary gj'mnosperms three out 

 of four genera are likewise now native to temperate North Amer- 

 ica, while the earlier Cretaceous genera representative of this 

 group are mostly extinct, though some are allied to existing fam- 

 ilies. The rich flora of the Tertiary, abounding in broad-leaved, 

 deciduous forests, must have developed under conditions far dif- 

 ferent from any that have existed since, both as to temperature 

 and moisture, and doubtless far more favorable for the origin 

 of new forms. 



The following lists from the works of Newberry (44), Les- 

 quereux (33), Knowlton (28) and Ward (69) are doubtless in- 

 complete but will serve to indicate something of the past history 

 of the flora of this region. The genera at present existing 

 here are marked by an asterisk (*). 



GYMXOSPEEMS 



Araucaria Glossozamites 



Sequoia Cycadnspcrmum 



02 



