No.i.} OKAY AND HOOKER ON THE ROCKY MOUNTAIN FLORA. 75 

 vives ; that W6 haw evidence, not merely Of 1'ines and Maples, Poplars. Birches, I- iii 



dens, and whatever else characterize tin- temperate-sone forests of our era, but also of 

 particular species of these, so like those of our own time and country thai we may fairly 

 reckon them as the ancestors of ><\ era! of ours. Long genealogies always deal mom 

 or less in conjecture, bat we appeal to be within the limits of scientific Lnferenoe when 

 w* announce that onr existing temperate trees came from tin- north, and within the 

 honmls ..t' oigh probability when we claim not a few of them as the originals of pres- 

 ent species. Remains of the same plants have been found fossil in our temperate re- 

 gion, as well ss in Europe* 



Here, then, we haw reached a fair answer to i be anest Ion, how I he same or similar 

 species of om trees came to be so dispersed over such widely separated continents. The 

 lands all diverge Gram a polar centre, and their proximate portions, however different 

 from their present configuration and extent, and however changed at different times, 

 were once the home «'t' those trees, where they flourished in a temperate climate. The 

 cold period which followed, and which doubtless came on by very slow degrees during 

 ages of time, must, long before its culmination, have brought down to onr latitudes, 

 with the similar climate, the forest they possess now, or rather the ancestors of it. 

 Daring this long (and we may believe first) occupancy of Europe and the United 

 States were deposited in pools and shallow waters the east leaves, fruits, and, occa- 

 sionally, branches, which are embedded in what are called Miocene Tertiary, or later 

 deposits, most abundant in Europe, from which the American character of the vege- 

 tation of the period is inferred. Geologists give the same name to these beds in 

 (ireenlaiul and Southern Europe, because they contain the remains of identical and 

 very similar species of plants, and they used to regard them ss of the same age, on 

 account of this identity. But in fact this identity is good evidence that they cannot 

 be synchronous. The beds in the lower latitudes must be later, and were forming 

 when Greenland probably had very nearly the climate which it has now. 



Wherefore the high, and not the low, latitudes must be assumed as the birth-place 

 of our present flora :* and the present arctic vegetation is best regarded as a derivative 

 of the temperate. This rlora, 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 en- 

 dowment 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 conti- 

 nents, and on their different sides, in a way which might well account for the present 

 diwi-iiiration. From an early period the system of the winds, the great or. an (or- 

 ients however they may have oscillated north andsoutb), and the general proportions 

 and features of the continents in OUT latitude | at least of the American conf im-nt ) 



much the sain, as now. so that species ot' plants, ever so little adapted or pre- 

 disposed to <(»ld winters and hot summers, would abide and be developed on the east 

 cm si, i,. of. ontinents, therefore in the Atlantic United States and in Japan ami Man- 

 churia: 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 sum- 



tin. Bo that if the same thousand species were thru t promiscuous]; into these 

 -. and carried slowly onward in the way supposed, they would inevit- 

 ably be sifted in Mich a manner that the sun ival of the fittest for each district d 

 explain the present diversity. 



Besi d es, there are : to take into the account. The glacial period or refrig- 



eration from the north, which at its. inception forced the temperate flora into om 



*Thista] mted, aftea skiold, that there «;i- n<> precedi 



. as neithei paleontology nor the study ,.t arctic sediments l any 



evidence «-t it. Ch if there were an] Bmote in time to concern the pi 



question. 



