CLASSIFICATION OF ARKOSE DEPOSITS 445 



The arkosic beds are best developed about the granitic masses of 

 the eastern margin, but reappear from horizon to horizon with 

 increasing marks of water-wear. The arkose of the basal horizons 

 is granitic in appearance, and by the inexpert eye might not be 

 distinguished from the granite. The arkose is gray in color and 

 is composed of subangular grains of quartz and much decomposed 

 feldspar in an argillaceous matrix of small amount. The arkose of 

 the higher horizons is not so granitic in appearance, there is a 

 somewhat lower content of feldspar, and the quartz and feldspar 

 grains are slightly more rounded. Some of the associated shale 

 beds are carbonaceous, and locally there are small intercalations 

 in the arkose of carbonaceous silty material. 



To this type of deposit there should probably be referred: 



The Carboniferous arkose of the Narragansett Basin, Rhode Island and 



Massachusetts 

 The arkose of the Rockwell formation (Mississippian), Meadow Branch 



Mountains, West Virginia 

 The arkose of the Vosges Mountains, the Black Forest, and adjacent 



parts of Bavaria 

 The arkose of the Coal Measures of the Yorkshire Coal Field, England 

 The arkose of the Coal Measures of the Flint, Rhutin, and Mold districts, 



England 

 The arkose of the Richmond (Triassic) Coal Basin, Virginia 

 The arkose of the Corwin formation (Jurassic), Alaska 

 Comanchean arkose at the base of the Coastal Plain series, Maryland, 



Virginia, North Carolina 

 The arkose of the Swauk formation (Tertiary), Washington 

 The arkose of the Puget formation (Tertiary), Washington. 

 The arkose (Early Tertiary) of the Matanuska and Controller Bay regions, 



Alaska 



c) Deposits formed under glacial conditions: If an ice sheet 

 advances over a granitic terrane in which there is a mantle of dis- 

 integration, it would seem possible for small amounts of this debris 

 locally to be preserved as arkose among the various glacial deposits. 

 In New England, there is in several localities deep preglacial dis- 

 integration, showing that the mantle of disintegration of the 

 Piedmont district probably extended in former times northward 

 over this area. Arkose is apparently lacking however, in the New 

 England glacial deposits. No example of this type of deposit is 

 known to the writer. 



