446 DONALD C. BARTON 



2. Marine and lacustrine, -(a) The basal member of a new, 

 transgressive marine series is commonly composed of the materials 

 of the former regolith. If the shore forces are not too violent in 

 their working over of the debris, the basal deposit in regions of 

 granitic rocks may be arkosic. The constituent grains show more 

 or less rounding. There may be present a small amount of argil- 

 laceous matrix. Through the elimination of the feldspar the arkose 

 may grade into quartzite. Arkose deposits of this type may grade 

 into deposits of the type discussed in (b) . 



To this type of deposit (a) there should be apparently referred: 



Arkose of the llotauto formation (pre-Cambrian), Shinumo Quad., Arizona. 



The Cambrian arkose of Eastern United States (in large part) 



The arkose (Silurian) of Littleton, New Hampshire (in part) 



The arkose of the Igaliko formation (Devonian), Greenland 



The arkose (Triassic) of the Morvan (in part), France 



The arkose (Tertiary) of the Limagne (in part), France 



(/>) When erosion of the mantle of disintegration in a granitic 

 terrane adjacent to the sea or to a lake occurs, deposition of the 

 disintegrated material is likely to take place in the sea or lake with, 

 as a consequence, the formation of arkose. Near the shore the 

 arkose is in banks and lenses and is interstratiried with beds com- 

 posed of the material from the soil and zone of decomposition and 

 of argillaceous material eliminated from the debris of disintegration. 

 The constituent grains of the arkose are subangular to poorly 

 rounded, the degree of rounding being greater in the more quartzose 

 beds. There may in some cases be a slight amount of argillaceous 

 matrix. Unless the feldspar is itself reddish, the arkose is 

 grayish in color. Although not necessarily basal, the arkose is 

 more likely to be near the base of the formation than not, since 

 the change of conditions which causes the erosion of the mantle 

 of disintegration is likely to mark the inauguration of a new period 

 of sedimentation. The arkose formed far from shore is less granitic 

 in appearance than that formed immediately at the shore, there is 

 considerable rounding and sizing of the constituent grains, and there 

 is elimination of much feldspar and argillaceous material. The 

 arkose in many cases grades into quartzite. 



An example of this type of deposit is the Tertiary arkose of the 

 Limagne, France. During the Oligocene times the Limagne was 



