1890 .] 
171 
[Uphatn. 
to have made the shores of that land more inhospitable since its 
first colonization by Scandinavians, only about nine hundred years 
ago. On the shores of Iceland, Scotland, northwestern Europe, 
and Spitzbergen, similar isolated southern marine shells are also 
found, either still living or fossil in postglacial deposits, and the 
successive floras fossil in the peat-bogs of the land likewise tell of 
a formerly milder climate, as well summarized by Prof. James Geikie 
in his ‘‘Prehistoric Europe.” 
But no such evidences of climatic alternations since the Glacial 
period are discovered in the interior region of this continent, as in 
the range of species of plants in the Red river basin. Instead, we 
see there, in the southern stations of boreal species, indications of 
the gradual amelioration of the climate through the postglacial ep- 
och to the present day. In Siberia, too, the frozen bodies of mam- 
moths show that a continuously cold but probably ameliorating 
climate has been uninterrupted by any warm interval since the Gla- 
cial period. The recently warmer climate of the northern Atlan- 
tic countries, from New England to Greenland, Iceland, Scandinavia 
and even Spitzbergen, seems therefore referable to formerly greater 
volume of the warm Gulf Stream, rather than to any astronomic 
conditions, which would affect not only that ocean and its shores 
but also the central and northwestern portion of our continent and 
northern Asia. 
Besides the greater part of our flora which is of northern origin, 
coming to us from an ancestral flora that probably in the begin- 
ning of the Quaternary period occupied continuous land around 
the globe in high northern latitudes, the plants of the Red river 
basin include many species derived, as Gray and Watson have 
shown for a large portion of the flora of California, the Great Ba- 
sin, and the southern Rocky Mountain region, from the plateau veg- 
etation of Mexico. By the return of a warmer and drier climate 
in the southwestern United States, following the Ice Age of the 
north, our Cactus species, Petalostemons, and Onagracese, many 
of our Compositse, the milkweeds, and many more, have been en- 
abled to spread from their original southwestern and Mexican home- 
land, becoming a most important element of the flora of all the 
plains and prairie region to the Saskatchewan and Red rivers, and 
gaining a less numerous representation in the wooded country east 
to the Atlantic coast. 
