THE ORIGIN OF RED BEDS 17 1 



all the sediments of the series, it would cause gray and green colors 

 in the sands rather than in the muds, by reason of the mechancial 

 concentration of ferric oxide in the latter. The ratio of ferruginous 

 materials to organic matter seems to be the dominating factor in 

 determining the colors of ferruginous beds. Barren's second 

 suggestion in the foregoing quotation, dealing with this point, 

 deserves more careful investigation. 



Much of the organic matter carried as sediment in surface 

 waters tends to be concentrated with the muds, for reasons analo- 

 gous to those already suggested in the case of ferruginous material 

 (i.e., fine division) ; but the proportion so concentrated is probably 

 smaller in the case of organic matter than in that of ferruginous 

 material, because of the indiscriminate distribution of driftwood, 

 the growth of vegetation in most regions of clastic deposition, and 

 other similar factors. In any of these cases organic matter in 

 large quantities may enter into the composition of sands and muds 

 alike, and thus bring about a higher ratio of organic to ferruginous 

 matter in the sands than in the muds. 



These controlling factors are so complex that no constant rela- 

 tion between coarseness of grain and distribution of organic matter 

 is to be expected. It is evident from the quotations on p. 170 that 

 definite organic remains in the section there under consideration are 

 confined chiefly to gray and green strata; and it is also evident 

 that such strata include both shales and sandstones. An examina- 

 tion of the detailed section 1 of the Catskill formation published by 

 Barrell in this paper reveals a somewhat less uniform relation 

 between coarseness of grain and color of beds than one would 

 understand to be the case from reading the text or the labels on 

 the graphic columnar section. 2 Of the 3,864 feet of beds definitely 

 described as of one or the other type, 2,179 feet (56.4 per cent) 

 bear out Barrell's generalization that gray and green colors are 

 typical of sandstones and red colors of shales, 901 feet (23.3 per 

 cent) are noncommittal, and 754 feet (20.3 per cent) are in opposi- 

 tion to the rule. This variability is in better accord with the com- 

 plexity of the factors controlling the distribution of organic matter 

 in sediments than a more constant relation would be; and suggests 



1 Barrell, op. cit., pp. 4S x -5 6 - 2 Ibid -> P- 457- 



