CLASSIFICATION OF ARKOSE DEPOSITS 439 



the amount that takes place in this manner is slight. If disintegra- 

 tion takes place, the conditions would seem favorable to the erosion 

 of the disintegrated material and its deposition in arkose deposits 

 of small or moderate size, probably in association with glacial or 

 fluvioglacial beds. To this type of deposit may possibly be referred 

 some of the pre-Cambrian arkose of Canada. 



B. DEPOSITS FORMED DIRECTLY OR INDIRECTLY THROUGH THE 

 EFFECTS OF MOIST AND USUALLY TEMPERATURE CONDITIONS 



Deposits of small or moderate size; the arkose commonly with 

 a matrix of fine-grained argillaceous material and usually associated 

 with argillaceous beds; feldspars commonly showing a moderate 

 amount of decomposition (Fig. 4). 



In the present regions of moist temperate climate, especially 

 where the topography is in a mature or old-age stage of develop- 

 ment, there is almost universally present a very considerable 

 accumulation of disintegrated material which is available as a 

 source of material for the formation of arkose. The following 

 section, from the vicinity of Autun, France, in its essential features 

 is characteristic of such regions as the granite terranes of Morvan, 

 the Plateau Central, and Forez, France; the Vosges Mountains, 

 the Odenwald, and the Thiiringerwald, Germany; Dartmoor, 

 England; the Piedmont belt and the Pike's Peak region, United 

 States. 



1 ft Mantle of vegetation; surface soil and subsoil of 



gritty brown clay with quartz and feldspar grains 



6ft Granitic sand and gravel, stained with limonite ; feld- 

 spar showing considerable decomposition toward the 

 surface, the amount decreasing with depth 



2+w ft Granite more or less fresh on superficial examination, 



but crumbling under light blows of the hammer; 

 depth difficult to estimate; fresh granite 



The relative and absolute proportions of these zones vary greatly. 

 The maximum depth to which disintegration was observed by the 

 writer to have extended was 40 feet, at Royat (Puy-de-D6me), 

 France, and at Hohkonigsburg, Vosges Mountains. On Dartmoor 

 and in the Piedmont belt decomposition is more in evidence than 

 in France and, in the Piedmont belt especially, the zone of soil and 



