CLIMATE AND TERRESTRIAL DEPOSITS 267 



the iron may be deoxidized and concentrated, but not eliminated. 

 The colors of the deposits are consequently white or black or gray. 

 These opposed relations of carbon and iron and the leaching of soluble 

 components from the fire-clays underlying swamp deposits as derived 

 from the study of modern instances are seen to correspond to the nature 

 of the coal-measures and the conditions of moisture necessary for 

 their formation have long been emphasized, but the added condition 

 of coolness as favoring more extensive accumulations of carbonaceous 

 character has not until within the past few years been generally recog- 

 nized. The great influence of coolness was perhaps first pointed out 

 by Russell, who in connection with the carbonaceous deposits of Alaska 

 expresses the following opinion : 



A possible origin of coal seams. — So vast is the amount of vegetable matter 

 now imprisoned in the tundra of the North, that I venture to suggest that possibly- 

 some coal seams may have had a similar origin. 



This suggestion does not seem so very unreasonable when one remembers 

 that except in the circumpolar tundra, deposits of vegetable matter are nowhere 

 accumulating at the present day to anything like the extent or thickness required 

 for the formation of coal fields like the one, for example, of which Pennsylvania 

 still retains a remnant. Botanists will say at once, in opposition to this sugges- 

 tion, that the flora of most of our coal fields, and especially those of Paleozoic 

 age, indicate tropical or sub-tropical conditions. The flora of the tundra, how- 

 ever, like the plants of the Carboniferous, is essentially and characteristically 

 cryptogamic. Two species of Equisetum, which may be considered as repre- 

 senting the Calamites of former times, flourish with rank luxuriance over great 

 areas along the Yukon.' ; 



It is further desired at this place to call attention to the other 

 chemical characters of the deposits, by which even without the pres- 

 ence of carbon the rainy nature of the climate may be inferred. Vari- 

 ous investigators have shown that in those portions of tropical soils 

 leached by heavy rainfall which are soluble in hydrochloric acid 

 soda is quite absent, potash is low, the residual soils usually not 

 possessing over o.i per cent.^ of potash and the river alluvium not 

 over 0.2 to 0.3 per cent.,^ the leached alluvium of Assam, a region of 

 extremely heavy rainfall, containing but] about wne-hah the potash 

 of the drier soils of the Indo-Gangetic plain. The same characteristics 



1 Op. cit., pp. 127, 128. 



2 E. W. Hilgard, Soils, 1906, p. 355. 



3 Op. cit., pp. 412, 413. 



