1 72 C. W. TOM LIN SON 



that even here the distribution of organic matter may be a con- 

 trolling influence in determining the colors of the individual strata. 



Dawson, 1 in discussing the Triassic ( ?) Red Beds of Nova 

 Scotia, says of the gray sandstones and shales interstratified with 

 them, that ''where thick, they always contain either fossil plants, 

 bituminous matter or thin seams of coal, or all of these. The fol- 

 lowing sentence from Geikie, 2 relative to the Old Red Standsone of 

 the British Isles, is also interesting in this connection: "It may be 

 observed also that where gray shales occur intercalated among the 

 red sandstones and conglomerates they are often full of plant 

 remains, and may contain also ichthyolites and other fossils which 

 are usually absent from the coarser red sediments." 



Organic matter the controlling influence in the case of the western 

 Red Beds. — -Nowhere in the literature on the western Red Beds is 

 there suggested such a definite and relatively constant association 

 of green and gray colors with sandstones, and of red with shales, 

 as that which Barrell sees in the Catskill formation, and as that 

 which is described as occurring in the Siwalik formation of India. 3 

 In the foregoing quotation from Geikie, the opposite relation is 

 implied in the Old Red Sandstone series of Great Britain. In the 

 Red Beds of the western United States variegation is perhaps more 

 common in shales than in sandstones, though it occurs to a marked 

 extent in both. 4 The distribution of gray and green colors in 

 the Red Beds coincides very closely with the distribution of organic 

 remains in the same series, in so far as such remains are present; 

 and this close association, together with the chemical probabilities 

 of the case, suggest that organic remains now obliterated explain 

 at least the greater part of the remaining gray and green areas and 

 strata. The decolorization of these sediments may, therefore, 

 have been complete before their burial under later strata. The 



'J. W. Dawson, "On the Colouring Matter of Red Sandstones and of Greyish 

 and White Beds Associated with Them," Quar. Jour. Geol. Soc. London, V (1S4S), 

 25-30. Quotation from p. 26. 



2 Geikie, op. cit., p. 1003. 



1 Medlicott and Blanford, A Manual of the Geology of India, II (1879), 5 2 4~ 2 6- 

 Quoted by Barrell, op. cit., pp. 463-64. 



4 Cf. Permian of the Pecos Valley and of the Zuni and Colorado plateaus; and 

 the Jura-Trias Painted Desert sandstone of the latter plateau. 



