FLIGHT OF PLANTS AND ANIMALS. 435 



sunshine — their ample extent north and sonth, their diversified 

 configuration, their proximity to the great Pacific Gulf Stream, 

 by which a vast body of warm water sweeps along their accentu- 

 ated shores, and the comparatively equable diffusion of rain 

 throughout the year, all probably conspire to the preservation 

 and development of an originally ample inheritance. 



The case of the Pacific forest is remarkable and paradoxi- 

 cal. It is, as we know, the sole refuge of the most character- 

 istic and wide-spread type of Miocene Coniferce, the Sequoias; 

 it is rich in coniferous types beyond any country except Japan ; 

 in its gold-bearing gravels are indications that it possessed, 

 seemingly down to the very beginning of the Glacial period, 

 Magnolias and beeches, a true chestnut, Liquidambar, elms, 

 and other trees now wholly wanting to that side of the conti- 

 nent, though common both to Japan and to Atlantic North 

 America. Any attempted explanation of this extreme paucity 

 of the usually major constituents of forest, along with a great 

 development of the minor or coniferous element, would take 

 us quite too far, and would bring us to mere conjectures. 



Much may be attributed to late glaciation ; something to 

 the tremendous outpours of lava which, immediately before 

 the period of refrigeration, deeply covered a very large part of 

 the forest area ; much to the narrowness of the forest-belt, to 

 the want of summer rain, and to the most unequal and pre- 

 carious distribution of that of winter. 



Upon all these topics questions open which we are not pre- 

 pared to discuss. I have done all I could hope to do in one 

 lecture if I have distinctly shown that the races of trees, like 

 the races of men, have come down to us through a prehistoric 

 (or pre-natural-historic) period ; and that the explanation of 

 the present condition is to be sought in the past, and traced in 

 vestiges, and remains, and survivals ; that for the vegetable 

 kingdom also there is a veritable archaeology. 



As the truth of a theory needs to be tested by the meth- 

 od of difference as well as of agreement, we turn to inquire 

 if it be not true that all mountains which reach above the 

 snow-line have an Alpine flora, and whether it be not the 

 conditions themselves which determine the peculiarities? 



