64 FOREST DISTRIBUTIOlSr 



Iceland to Greenland and Kamtehatka a mild temperate c-limate 

 prevailed and forests like those from New England to Virginia 

 and California clothed the land. In the words of (jray (20) : 

 ' ' We appear to be within the limits of scientific inference when 

 we announce that our existing temperate trees came from the 

 north." All species were probably crowded southward by the 

 ice and doubtless found at least a narrow zone suited for their 

 occupation during the period of glaeiation. Upon the retire- 

 ment of the ioe some of these species or their descendants must 

 have reoccupied portions of the land. During all of this period 

 selective influences were undoubtedly sifting out the species 

 which were the distant forebears of our present flora. Climatic, 

 topographic, and edaphic conditions determined the final types 

 of vegetation (prairie, forest, etc.) over large areas of the land 

 reoccupied. Since none of the existing species of this region, 

 as far as we know, have appeared in the Tertiary deposits it 

 seems probable that they have entered or evolved since that 

 period. 



The present alpine flora of the northern Rockies shows 

 little evidence of its connection with the Tertiary flora above 

 mentioned. Few species are common to the old and new world, 

 and no closely related forms are here known in the fossil state. 

 Rydberg (5.5) mentions one woody plant, a dwarf willow (Sa'ix 

 reticulata) as common to the arctic regions of both continents 

 and to the higher altitudes of the Alps and the Rockies. 



Beyond a few other shrubby willows and heaths, with aftin- 

 ities more or less evident with European species, immediate con- 

 nection between the woody alpine flora of this region and that 

 of the old world can hardly be admitted. As to some of the sub- 

 alpine species (admitting the difference of opinion as to the 

 identity of the old and new world forms of Junipenis Sabina 

 and communis a few may be cited as having general circum- 

 polar distribution in the pre-glacial period. Probably a consid- 

 erable number of plants may be regarded as indigenous to the 

 northern Rocky Mountain region .since the glacial period. Cer- 

 tain species considered by some to be transcontinental are by 

 others divided into two or more species with lesser ranges con- 

 tiguous or overlapping ; without considering the merits of thise 



