SEQUOIA AND ITS HISTORY. 217 



grees of emphasis, and, if to be explained at all, will 

 have the same kind of explanation. 



Continuing the comparison between the three re- 

 gions with which we are concerned, we note that each 

 has its own species of pines, firs, larches, etc., and of 

 a few deciduous-leaved trees, such as oaks and maples ; 

 all of which have no peculiar significance for the pres- 

 ent purpose, because they are of genera which are 

 common all round the northern hemisphere. Leaving 

 these out of view, the noticeable point is that the vege- 

 tation of California is most strikingly unlike that of 

 the Atlantic United States. They possess some plants, 

 and some peculiarly American plants, in common — 

 enough to show, as I imagine, that the difficulty was 

 not in the getting from the one district to the other, 

 or into both from a common source, but in abiding 

 there. The primordially unbroken forest of Atlan- 

 tic Xorth America, nourished by rainfall distributed 

 throughout the year, is widely separated from the west- 

 ern region of sparse and discontinuous tree-belts of the 

 same latitude on the western side of the continent 

 (where summer rain is wanting, or nearly so), by im- 

 mense treeless plains and plateaux of more or less 

 aridity, traversed by longitudinal mountain-ranges of 

 a similar character. Their nearest approach is at the 

 north, in the latitude of Lake Superior, where, on a 

 more rainy line, trees of the Atlantic forest and that 

 of Oregon may be said to intermix. The change of 

 species and of the aspect of vegetation in crossing, say 

 on the forty-seventh parallel, is slight in comparison 

 with that on the thirty-seventh or near it. Confining 

 our attention to the lower latitude, and under the 



