144 University of California Piiblicatio-ns in Zoology [Vol.24 



The Sitkan district of southeastern Alaska is characterized by- 

 excessive humidity and by relatively equable temperature. The annual 

 rainfall at many points is 100 inches or more, the number of rainy 

 days per year around 200. There is a great deal of foggy and cloudy 

 weather. The winters are not extremely cold nor are the summers 

 very warm. The vegetation of this region is comprised mostly of an 

 extremely dense growth of coniferous forest trees, and, beneath the 

 trees, underbrush almost tropical in its luxuriance. The Sitkan dis- 

 trict is here considered as including the islands between Cross Sound 

 and Dixon Entrance, together with a narrow strip of the adjacent 

 mainland coast. Its eastward limits are sharply defined by the tower- 

 ing and precipitous range of mountains that, rising abruptly from 

 the shore, parallels the coast. To the eastward of this Coast Range, in 

 the interior of British Columbia and Alaska, is a region of widely 

 different character. I have not exact meteorologic data for this section, 

 but certain general facts are obvious. Dawson (1889, pp. 58&-59&) 

 remarks on this subject as follows : 



It may be stated here, as sho-ndng the broad general contrast, that while the 

 annual precipitation at Wrangell, at the mouth of the Stikine, is over sixty inches, 

 that m the vicinity of Telegraph Creek on the inland side of the mountains, is so 

 small that it is necessary to irrigate cultivated land. Nor does this comparison 

 of rain-fall sufficiently mark the great diversity vphich actually obtains between 

 the two climates, the prevalence of clouded skies in the coast region being accom- 

 panied by a saturated state of the atmosphere, while precisely opposite conditions 

 are found on the eastern side of the mountain belt, at not more than eighty miles 

 inland from the general line of the coast. 



The country east of the mountains is subject to far greater extremes 

 of temperature than the coast region, with hot summers and with ex- 

 tremely cold winters. The forell covering includes a considerable pro- 

 portion of conifers, but there is also a still larger proportion of de- 

 ciduous timber. The animal life in these two regions, the Sitkan 

 district of the coast and the adjacent interior, is widely different. 



The valley of the Stikine forms a highway between the two faunal 

 areas, otherwise separated by physical barriers and sharply contrasted 

 in nearly all particulars, though lying in close juxtaposition. The 

 presence of this channel of communication affords excellent oppor- 

 tunity for observation of the geographic behavior of the many animal 

 species that by this means are permitted an outlet in either direction. 

 Certain contrasted species and subspecies occupying comparable posi- 

 tions in each of the two faunal areas are brought together, and thus 

 into competition ; others with no such direct rival in the adjacent area 

 are brought into contact with climatic conditions, adverse in that they 

 are unaccustomed. 



