THE ORIGIN OF RED BEDS 167 



afford the least ready passage to water, as is actually the case. 

 The cementing material of the Red Beds, in so far at least as it is 

 ferruginous — and the remainder of it has little or no bearing upon 

 the point in question — was therefore for the most part present in 

 those beds at the time they were deposited as sediments. 



Extent of known secondary redistribution of coloring matter. — 

 Although the evidence is convincing that the ferruginous matter in 

 the Red Beds was an integral part of the original sediment, and 

 that it was deposited originally in the series in practically its present 

 distribution and arrangement, it is equally certain that there have 

 been some later modifications of that primary distribution. A 

 large majority of all variations of color within the Red Beds are 

 limited by bedding planes; but there are numerous minor varia- 

 tions in color due to the migration of coloring matter along the 

 lines of movement of ground-water. 1 Reducing solutions locally 

 extract ferruginous matter along joints, or cause a general down- 

 ward movement of iron. In the western Red Beds, as in Barrell's 

 section of the Catskill formation in Schuylkill County, Pennsyl- 

 vania, 2 the lower boundaries of many deeply stained bands are 

 drawn less sharply than the upper. All of these are very minor 

 features, however, in the distribution of the coloring matter of the 

 series as a whole. The analyses (p. 161) furnished by Blackwelder 

 illustrate the effect of leaching along a joint; the color changes from 

 red to greenish, the net iron content is reduced from 3.26 per cent 

 to 1 . 53 per cent, and the ratio of ferric to ferrous iron drops from 

 3 . 02 : 1 . 00 to o . 89 : 1 . 00. 



IS THE FERRUGINOUS MATERIAL IN THE SAME FORM AS AT THE 

 TIME OF SEDIMENTATION? 



Variations in degree of oxidation. — -Is the color due to recent 

 oxidation in weathering ? It has sometimes been asserted that the 

 color of the Red Beds is a superficial matter, due to the weathering 

 of originally dull-colored sediments. In support of this idea drill 

 records have been quoted, showing that beyond a certain depth 



1 Cf. Richardson, op. cit., p. 376. 



2 See Joseph Barrell, "The Upper Devonian Delta of the Appalachian Geo- 

 syncline," Am. Jour. Sci., 4th Ser., XXXVI (1913), 437 ff- 



