266 TIME CONSIDEEATIONS 



by the fact that disintegration increases so rapidly with altitude 

 that the rate of uplift may not exceed that of degradation. 



Relative to the subject of rock degeneration in temperate re- 

 gions, we have to consider the possible increased amounts of 

 atmospheric gases brought down by snowfalls, over those brought 

 by rain. The snowfiakes so completely fill the air as to rob it of 

 a larger proportion of its impurities than would a corresponding 

 amount of precipitation in the form of rain. Further, the snow 

 in melting affords the water better facilities for soaking into the 

 ground than though the same amount was poured down during 

 the comparatively brief period of a shower. How far these 

 agencies may go toward counterbalancing the effects of the con- 

 tinued higher temperatures of the tropics, we have no means of 

 judging.^ 



Influence of Forests. — It is even questionable if decomposition 

 has actually gone on to greater depths in regions covered by 

 forests, as contended by Hartt^ and Belt^ than elsewhere. Indeed 

 observations by geologists of the Egyptian Survey* are to the 

 effect that rock degeneration has proceeded at a fairly rapid rate 

 in regions completely lacking in forest growth. The high granite 

 ridge, bordering on the Red Sea, is described as ''remarkable for 

 the number of sharp, ragged peaks it shows and bounded in 

 many cases by almost sheer precipices which are rendered in- 

 accessible on account of the rotten nature of the rock.'' The 

 accumulation of a large amount of organic matter is undoubtedly 

 favorable to decomposition, but the growing vegetation constantly 

 robs the soil beneath of moisture and other elements necessary 

 for its growth, storing it away in the form of woody fibre or 

 sending it off into the atmosphere once more. The amount of 

 moisture that a full-grown tree evaporates daily through its 

 leaves is simply enormous, and is often made conspicuously ap- 

 parent by the dry knolls that may be seen surrounding isolated 

 trees or groups of trees in swampy areas. Indeed, Mr. R. L. 

 Fulton, in discussing^ the influence of forests in the mountain 



1 There is an old saying among Eastern farmers to the effect that a late 

 spring snowstorm is as good as a dressing of manure. It undoubtedlj arose 

 from an appreciation by the farmers of the fact that the snow was more 

 beneficial than rain for the reasons above mentioned. 



2 Physical Geography and Geology of Brazil. 



3 The JSTatnralist in Nicaragua, p. 86. 



* Geological Survey Beport, Cairo, 1902, p. 62. 

 fi Science, April 10, 1896. 



