CLIMATE AND TERRESTRIAL DEPOSITS 265 



to fall at the slightest touch. ^ .... The entangled mass of the thriving and 

 the fallen reminded me of the forests within the tropics — yet there was a differ- 

 ence: for in these still solitudes, death, instead of life, seemed the predominant 

 spirit. 2 



These statements bring into prominence the slowness of organic 

 decay in cool climates and its rapidity in warm, permitting the accumu- 

 lation of dead vegetable matter in the one region, quickly removing 

 it from view in the other. Schimper also calls attention to the relative 

 poverty of humus in tropical soils and emphasizes the statement that 

 peat is never produced in the tropics except on mountains over 

 1,200 meters in height.^ 



Influence of arctic climates. — Within the colder portions of the 

 temperate zones a lesser rainfall and severer winters result in a some- 

 what diminished luxuriance of vegetation, but, as previously noted, 

 on account of the less intense evaporation and oxidation notable 

 deposits of carbon may still result. In the interior of Alaska the pre- 

 cipitation varies from about ten inches per year on the eastern bound- 

 ary to about twenty-five inches per year where the interior province 

 passes on the west into the relatively humid Behring Sea province. 

 The heaviest precipitation is in summer, but is always moderate in 

 amount. 4 Under these conditions of rainfall, which in a hotter 

 climate would lead to aridity or semiaridity, there is here found on 

 the lowlands, where these are within the timber line, a luxuriant 

 forest of spruce and willow with an undergrowth of cryptogamic 

 character. 



Within the Arctic Circle beyond the limit of arboreal vegetation 

 exist the vast treeless moss-covered plains known as the tundra, per- 

 petually frozen below the depth of a foot or two. In the far north the 

 tundra may be developed under a rainfall of not over ten inches per year, 

 but in such regions the vegetation is meager and barely covers the 

 soil. Farther south, however, and in more rainy districts a thick 

 carpet of peaty vegetable matter may accumulate. A tundra of this 

 character is found on the delta of the Yukon under a rainfall of from 



1 "Ascent of Mount Tarn," The Voyage 0} the Beagle, June, 1834. 



2 Ibid., "Scenery of the Mountains and Retrospect." 



3 Plant Geography, 1898 (Eng. trans.), pp. 381, 382. 



4 Cleveland Abbe, Jr., "Climate of Alaska," pp. 147, 154-157, Professional 

 Paper No. 45, U. S. Geological Survey, 1906. 



