FOREST GEOGRAPHY AND ARCHEOLOGY. 229 



Wherefore the high, and not the low, latitudes must be 

 assumed as the birthplace of our present flora ; 2 and the 

 present arctic vegetation is best regarded as a derivative of 

 the temperate. This flora, which when circumpolar was as 

 nearly homogeneous round the high latitudes as the arctic 

 vegetation is now, when slowly translated into lower latitudes, 

 would preserve its homogeneousness enough to account for 

 the actual distribution of the same and similar species round 

 the world, and for the original endowment of Europe with 

 what we now call American types. It would also vary or be 

 selected from by the increasing differentiation of climate in 

 the divergent continents, and on their different sides, in a way 

 which might well account for the present diversification. 

 From an early period, the system of the winds, the great 

 ocean currents (however they may have oscillated north and 

 south), and the general proportions and features of the conti- 

 nents in our latitude (at least of the American continent) 

 were much the same as now, so that species of plants, ever so 

 little adapted or predisposed to cold winters and hot summers, 

 would abide and be developed on the eastern side of conti- 

 nents, therefore in the Atlantic States and in Japan and 

 Mandchuria ; those with preference for milder winters would 

 incline to the western sides ; those disposed to tolerate dryness 

 would tend to interiors, or to regions lacking summer rain. 

 So that, if the same thousand species were thrust promiscu- 

 ously into these several districts, and carried slowly onward 

 in the way supposed, they would inevitably be sifted in such a 

 manner that the survival of the fittest for each district might 

 explain the present diversity. 



Besides, there are re-siftings to take into the account. The 

 Glacial period or refrigeration from the north, which at its 

 inception forced the temperate flora into our latitude, at its 

 culmination must have carried much or most of it quite be- 

 yond. To what extent displaced, and how far superseded by 



1 This takes for granted, after Nordenskjbld, that there was no pre- 

 ceding Glacial period, as neither palaeontology nor the study of arctic 

 sedimentary strata afford any evidence of it. Or if there was any, it 

 was too remote in time to concern the present question. 



