THE ORIGIN OF RED BEDS 179 



fact that chemical deposition of salts of iron is only exceptionally 

 an important process in earth metamorphism. Glauconite, the 

 most common of such deposits at the present time, is of such 

 peculiar nature as to be readily recognized where it occurs in older 

 sediments : it certainly is not involved to any appreciable extent in 

 the origin of the Red Beds. Bog iron ore, the only other common 

 type of ferruginous chemical precipitate at present, is connected 

 intimately, in origin, with abundance of vegetation and with 

 peculiar and limited topographic conditions; and although deposits 

 of this type are scattered over many parts of the world, none of them 

 is comparable in extent or in thickness to even the smallest of 

 the Red Beds areas. Furthermore, no deposits similar in textural 

 character to bog ores are known in the western Red Beds. 



In view of the facts above stated, it seems a safe conclusion 

 that the coloring matter of the Red Beds was transported and 

 deposited almost if not quite wholly as a mechanical sediment; 

 and, therefore, without danger of serious error, we may limit 

 investigations of possible conditions of origin of this coloring matter 

 to those which would produce it as a mechanical sediment purely. 

 This applies to the gray and green members of the Red Beds series 

 as well as to those in which the iron is present chiefly as ferric oxide ; 

 for if the ferrous iron in the former be explained as the result of the 

 action of organic matter deposited in those strata, 1 the ferruginous 

 matter may have been in the ferric form during transportation, 

 quite as well as in any other. 



1 See pp. 170-72. 



[To be continued] 



