624 



PRINCIPLES OF STRATIGRAPHY 



there is a constant alternation of red shales and greenish sand- 

 stones. The physical characteristics of the deposit and the absence 

 of marine and presence of land and fresh water organisms show 

 that this series was formed under fluviatile conditions similar to 

 those of the Siwalik. 



Lateral variation in color is also a frequent feature of older 

 deposits and can be explained by the contemporaneous beds now 

 forming in the Seyistan basin, where the oxidized subaerial de- 

 posits merge laterally into the unoxidized subaqueous or lacustrine 

 ones. The fossiliferous Permic limestones and shales of Kansas 

 may be traced southward into red sandstone and shales of the 

 same age in Oklahoma, the latter being practically unfossiliferous. 

 These red clays may be in part the residual clays from dissolved 

 limestones (Beede-7) and in part of clastic origin. Their high 

 state of oxidation suggests widespread subaerial deposition under 

 sufficiently arid conditions to permit the free influence of the 

 atmosphere. Lateral variation of a more irregular character is 

 shown in some Mesozoic clays, such as the Potomac group of the 

 Atlantic coast, and the Cretacic Atlantosaurus or Como beds of 

 Wyoming, and in the Tertiary beds of the Wind River and Big- 

 horn basins and elsewhere. In the Wasatch and Wind River 

 clays analyses have shown the iron content to be as follows ''Sin- 

 clair and Granger-52 :ii3) : 



Sinclair and Granger comment on these analyses as follows : "In 

 all the samples examined, the total iron in the red clays is in excess 

 of that present in the blue by 1.48 per cent, to 1.49 per cent. The 

 amount of ferrous iron in the blue Wasatch clay is less than that 

 present in the red, while in the mottled Wind River clay it is 



