THE ORIGIN OF RED BEDS 163 



strong evidence in support of this hypothesis, aside from that of 

 association with igneous rocks, and the discovery of various lines 

 of evidence (among those outlined below) in direct opposition to it, 

 however, caused it to fall into disrepute. In the case of the western 

 Red Beds there is not even the association with igneous rocks to 

 suggest such an explanation. There are no contemporaneous 

 igneous rocks in any part of the Red Beds group, and in the greater 

 part of the area in which the group occurs there are no later igneous 

 rocks known. In no case is there a relation comparable to that 

 in the Connecticut Newark. 



Where the effect of later intrusions upon Red Beds has been 

 observed carefully, that effect is not to heighten, but to destroy, 

 the red color. This action has been noted in the Tenmile district 1 

 and in the Anthracite-Crested Butte district, 2 Colorado. 



Later introduction of iron by meteoric waters. — -There is no 

 apparent reason why the Red Beds should have been favored by 

 post-sedimentational iron-bearing solutions while other clastic 

 series in the same region, both older and younger, were not stained. 

 It might be expected that the coloring matter would be most 

 abundant in the most pervious strata, especially along the lower 

 surface of such strata, where they are in contact with less pervious 

 rocks. It is quite true that color boundaries in the series follow 

 bedding planes very closely; but, unfortunately for the hypothesis 

 of later introduction, the more highly ferruginous strata of the 

 Red Beds are as a rule, and with few exceptions, the more impervi- 

 ous. As noted above (pp. 158-59), in a series of alternating sand- 

 stones and shales it is almost invariably the shales which are 

 deeper in color. 



Ferric hydrates are not being introduced into the Red Beds 

 strata along the present joint planes. The analyses of Chugwater 

 sandstone given on p. 161 (see also footnote) show a marked leaching 

 of iron along a joint. Nor is iron commonly concentrated along 

 joints in paler sediments underlying the Red Beds. 



1 S. F. Emmons, Tenmile District Special Folio (No. 48), Geol. Atlas of the U.S., 

 U.S. Geol. Survey, 1896. 



2 G. H. Eldridge, "Description of the Sedimentary Formations," Anthracite- 

 Crested Butte Folio (No. 9), Geol. Atlas of the U.S., U.S. Geol. Survey, 1894. 



