146 University of California Publioations in Zoology [Vol. 24 



far below the general level, some of them to within a mile or two of 

 the river. It cannot be such a very long period of time since ice 

 blocked the entire valley. In fact, there are today legends among the 

 Tahltan Indians of a time when an ice bridge still extended across 

 the Stikine at the Great Glacier, connecting ice masses that are now 

 perhaps four or five miles apart. Of course, as remarked by Dawson 

 (1889, p. 53&) about this same tale, it is impossible to determine 

 whether "this is a remembered fact or a fancied inference." (In this 

 connection see also Emmons, 1911, p. 15.) 



The hypothesis of a glacial blockade of communication between 

 the interior and the coast would imply the separate derivation of the 

 animal life of- each. That is, that there was invasion from the south- 

 ward on either side of the coast range, of the same or of different 

 species, as the ease might be. Doubtless, at a still later period, there 

 was invasion of certain species from the northward as well. Among 

 birds in particular detailed comparisons may be made (see fig P), 

 and upon comparing the avifauna of the interior and of the coast in 

 the Stikine region, it will be seen that not only are comparable eeologie 

 niches on either side of the mountains usually filled by different species 

 rather than subspecies, but that frequently the species are not espe- 

 cially closely related. Furthermore, among the few cases where two 

 subspecies of a species do occur abundantly on either side of the moun- 

 tains, there is hardly an instance where we were able to trace inter- 

 gradation along the connecting valley of the Stikine. In some few 

 cases where the birds were abundant enough for us to ascertain the 

 fact, it was evident that certain subspecies, at this particular point, 

 met as distinct species. All thi% argues for invasion from the south- 

 ward, on either side of the Coast Range, of bird species and subspecies 

 that met at a much later period along such channels as the Stikine 

 Valley. 



The intrusion of a range of high mountains was productive of 

 diverse climatic conditions in the two regions. This, in turn, resulted 

 in differences in the reestablished plant and animal life to a far greater 

 extent than would follow from the mere presence of a physical barrier 

 such as a mountain mass. Differences of temperature and of humidity 

 arose, so that at the present time the two areas, east and west of the 

 Coast Range, respectively, form strongly contrasted faunal areas (de- 

 pendent upon relative humidity), and they are somewhat different 

 zonally (dependent upon temperatures). 



At a considerably later period than that at which the regions on 

 oither side of the mountains became habitable, conditions in certain 



