CLASSIFICATION OF ARKOSE DEPOSITS 441 



conditions without the introduction of an arctic flora sufficiently 

 luxuriant to form anew the protective mantle of vegetation. A 

 marked increase of the rainfall, it was suggested by Shaler, might 

 be such that the streams would be competent to waste generally 

 the land surface. A marine transgression would necessarily result 

 in the working over of the materials of the regolith, irrespective of 

 the luxuriance of the mantle of vegetation, and might easily result 

 in the deposition of arkose. Forest fires are not uncommonly due 

 to lightning and often are effective agents of deforestation. It 

 would seem possible that a period of heavy rains following a 

 severe forest fire might result in the general erosion of the mantle 

 of disintegration. Upwarping of considerable amount would result 

 in an increase of the stream gradients, in an increase or decrease 

 of the rainfall, and in the lowering of the mean temperature. The 

 total effect might possibly be conditions favorable to the general 

 erosion of the mantle of disintegration. A very special cause is 

 to be found in volcanic activity of the explosive type, which not 

 uncommonly results in deforestation and desolation in limited local 

 area. Of this type of deposit, in which the arkose should be asso- 

 ciated with tuffs, there is at least one example, the Rotliegendes 

 arkose north of Heidelberg, Germany. 



In regions of youthful topography and considerable relief in a 

 moist temperate climate, there would seem to be no reason why 

 disintegration should not take place. That it is not seriously in 

 evidence is probably due to the fact that it is masked by block dis- 

 integration and by rapid erosion. If it does take place, the debris 

 that can be eroded at one time is of small amount and is lost through 

 decomposition of the feldspars or through intermixture with the 

 heterogeneous stream-borne sediment. 



In tropical regions, decomposition commonly prevails over 

 disintegration, but in two localities disintegration is reported as 

 occurring with but slight accompanying decomposition. The debris 

 in these cases, if eroded under normal conditions, would probably 

 be lost through decomposition, but if eroded under the conditions of 

 a marine transgression, or under the conditions of aridity, there 

 would seem to be a strong possibility that a deposit of arkose might 

 be formed. Except by means of a contained fauna or flora, such 



