CLASSIFICATION OF ARKOSE DEPOSITS 447 



first a brackish- water basin some thirty km. in width and later a 

 fresh-water lake lying then as now in the granite plateau of the 

 Plateau Central. The arkose is found chiefly near the base and is 

 found in banks alternating with greenish marl and in some cases 

 extending out a considerable distance from the edge of the basin. 

 Some of the arkose, especially that at Royat, is massive, coarse, 

 composed largely of good sized fragments of the coarse phenocrysts 

 of the underlying granite, and is extremely granitic in appearance. 

 The greater part of the arkose, however, is much finer, is more 

 quartzose, is composed of more-rounded grains, and grades into 

 quartzite. There is in some cases an argillaceous matrix, in some 

 cases a sericitic matrix, and, in some of the more quartzose phases, 

 there is very little matrix. There is a general even horizontal 

 stratification. Where cross-bedding is present in individual strata 

 it is usually of the simple foreset type. 



To this type of deposit are probably to be referred : 



Much of the pre- Cambrian arkose of Ontario 



Arkose of the Congo Series, French Hoeck, Cape Colony 



The Cambrian arkose, North Carolina-Tennessee 



Fitch Hill arkose, Silurian, Littleton, New Hampshire 



Haybes arkose and Weismes arkose (Devonian) Ardennes-Eifel District 



Arkose of the Gres bigarres and Gres vosgien (Triassic) of the Morvan 



region, France 

 Dolomitic arkose (Keuper), Franconia and Thuringia 

 Arkose of the Blasensandstein and Coburgerbausandstein (Keuper), 



eastern Palatinate 

 Lower Stampian-Sannoisian arkose (Oligocene), Limagne, Forez, and 



Roannais basins, France 

 Much of the Jura-Cretaceous arkose of southwestern Alaska 

 Arkose of the Cutler formation (Permian), Colorado (?) 

 Arkose of the Fountain and Lower Wyoming formations (Permian), 



Colorado (?) 



C. UNTRANSPORTED OR SEDENTARY ARKOSE 



Basal, unstratified deposits grading into the underlying granite. 

 When deposition begins in a district, the original regolitb, locally 

 may be buried before it has been eroded to any considerable extent. 

 It is thus possible for arkose to be formed without the usual inter- 

 mediate steps of erosion, transportation and deposition of the 



