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 North 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 



