COLORS OF CONTINENTAL CLASTICS 625 



slightly greater in the blue than in the red phase, but in neither 

 case does it seem possible to ascribe the blue color to ferrous oxide, 

 as this substance is far exceeded in amount by ferric iron, evidently 

 occurring in the blue clay in some other form than ferric oxide 

 (hematite), perhaps as a hydrous silicate. In the Wasatch clay 

 the red contains 1.41% more Fe^Og than the blue; in the Wind 

 River clay Fe.Og in the red phase is 1.67% greater than in the blue. 

 If this excess of iron is present in the form of hematite, as the red 

 color seems to show, it is possible that the remaining iron in the 

 red clay may be in the same form as in the blue ( a hydrous sili- 

 cate?) and that the blue color has been masked by the red pig- 

 ment." 



"The results of analysis seem to show that the blue color has 

 not been derived from the red by reduction of the iron as ordinarily 

 understood. The red color may have been derived from the blue by 

 conversion of the hypothetical silicate into carbonate by meteoric 

 waters, and the subsequent oxidation of these salts, or by the intro- 

 duction of iron compounds in solution and their concentration and 

 oxidation possibly under drier climatic conditions than existed 

 during the deposition of the blue clays. We favor the latter alterna- 

 tive and regard the coloration of the clays as a phenomenon con- 

 trolled by conditions active during the deposition of each individual 

 stratum (red or blue, as the case may be), and not by subsequent 

 or secondary changes. Lender the arid conditions which exist at 

 present over most of the W'ind River and Bighorn basins, the 

 blue clays show no tendency to weather red. The layer of weath- 

 ered mud-cracked clay on the surface of bad land slopes cut in the 

 blue clays is yellow from the hydrous oxide, limonite." (52:7/^, 

 116.) 



Original Red Color of Sediments. Whatever the case above 

 mentioned shows, it must not be overlooked that some sediments 

 when deposited already have a decidedly red color, or that this may 

 be acquired before burial. Soils washed from regions of extensive 

 laterite formation will be deposited as red sediments either on 

 land or in the sea. Such sediments may be carried great distances 

 from regions where they are formed to regions where their pro- 

 duction is prohibited by the local climatic conditions. Russell held 

 that the red sands of the Newark system Vk^ere deposited with a 

 coating of red iron oxide formed during decomposition. This con- 

 clusion may, however, be questioned. 



Desert sands not infrequently have their grains coated with 

 a thin deposit of iron oxide which often gives the sands a brilliant 

 color, as in the case of the carmine sands of the Nefud desert of 



