382 GEORGE B. RICHARDSON 



integration and resedimentation of pre-existing red beds. This 

 explanation, however, does not strike at the root of the matter, 

 and in accounting for the color of such extensive masses of red 

 beds as those in the western states is not applicable. For the 

 rocks under consideration an explanation is demanded of the 

 formation of original red beds. The following are the most 

 important theories that have been advanced : 



1. Water containing iron in solution percolating through 

 rocks may have the iron precipitated as hydrate by contact with 

 oxygen-bearing waters, or by other means. The hydrate thus 

 formed subsequently may become dehydrated to the more sta- 

 ble red hydrate or to the anhydride. John W. Judd'' in this 

 way, explained the red color of the Northampton sands. 



\ a. K variation of this method is the precipitation as iron 

 carbonate of the iron contained in percolating waters by replace- 

 ment of calcium carbonate with which the waters may come in 

 contact. Oxidation may later convert the carbonate to the red 

 iron oxide. ^ C. H. Smyth considers this one of the ways by 

 which the red Clinton ores were formed. 



2. Again, iron-bearing minerals in rocks on a land area may 

 be decomposed by acidulated surface waters and the iron taken 

 into solution as bicarbonate and transported to a body of water 

 in which sediments are being deposited. Contact with air would 

 ■convert the bicarbonate to ferric hydrate, which would be pre- 

 cipitated among the accumulating sediments.^ Subsequent 

 changes would dehydrate the iron precipitate to a stable red 

 pigment. By this process bog iron ores are now accumulating. 

 This explanation often has been appealed to in accounting for 

 the color of red rocks. A. C. Ramsay^ advocated such an 

 ■origin for the color of the New Red sandstone. Also Henry 

 Newton 5 applied this explanation, as his interpretation of the 



^Geological Magazine, Vol. VI, p. 221. 

 '^Ihid., p. 487. 



3 Also some algae have the power of precipitating ferric hydrate from certain iron 

 -solutions.- -R. Brauns, Chetniscke Mineralogie, 1896, p. 383. 



* Quarterly Journal of the Geological Society, Vol. XVII, p. 241. 



5 Henry Newton, Geology of the Black Hills of Dakota, 1880, p. 138. 



