444 DONALD C. BARTON 



Forest fires are another possible cause. They are very commonly 

 due to natural causes and often are effective agents of deforestation. 

 It would seem possible that a period of heavy rains following a 

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

 regolith. Upwarping of considerable amount, with the consequent 

 increase of stream gradients and lowering of the mean temperature, 

 if associated with decrease in the amount of the rainfall, might 

 possibly result in the general erosion of the regolith. 



While these causes are thus in doubt, the fact of the formation 

 of deposits under these general conditions seems to be indubitable. 

 There is a characteristic type of arkose deposit which is usually 

 associated with carboniferous beds or coal, which is itself carbona- 

 ceous or may even carry carbonized plant remains, and which there- 

 fore must have formed under moist climatic conditions. As the 

 feldspar shows much decomposition, as there is an argillaceous 

 matrix, and as the quartz and feldspar grains are distinctly angular 

 to subangular, the constituent materials of the arkose would seem 

 to have been derived from the debris of disintegration under moist 

 temperate conditions. The arkose, commonly in part, is coarse 

 and granitic in appearance and seems not to have been transported 

 far from the point of origin of its constituent material, and in part 

 usually is finer and less feldspathic, and seems to have been trans- 

 ported for a greater distance. Besides being associated with coal 

 beds, the arkose is associated with conglomerates, impure sand- 

 stones, and silty mudstones. Cross-bedding is common, and many 

 of the beds seem to be the result of rather rapid deposition. The 

 color of this type of arkose is gray. 



As an example of this type of deposit, there may be taken the 

 arkose of the Richmond (Triassic) Coal Basin in Virginia. The 

 lower portion of the section in the basin is as follows :* 

 Productive Coal Measures 500 ft. Interstratified beds of bituminous 



coal, black shale, feldspathic and 



micaceous sandstones 

 Lower Barren Beds 0-300 ft. Sandstones and shales under the 



coal beds, often with arkose 

 Boscabel Bowlder Beds 0-50 ft. Local deposits of bowlders of gneiss 



and granite 



1 N. S. Shaler and J. B. Woodworth, U.S.G.S. Nineteenth Ann. Rcpt., Part II 

 (1897-98), pp. 423-26. 



