i58 



C. W. TOMLINSON 



the. Red Beds of the San Juan region and of the Anthracite, Crested 

 Butte, and Tenmile quadrangles of Colorado. Alternation of 

 paler with darker and with brighter shades of red is remarked in 

 almost every occurrence of Red Beds. In all these instances it is 

 significant that the color boundaries tend to follow bedding planes, 



Percent 



Fig. 2. — Diagram to illustrate the relation between color and the proportion of 

 ferric to ferrous iron in ferruginous slates. Analyses (from Dale) are lettered to 

 correspond with text'. 



and usually accompany changes in coarseness of grain. Many of 

 the color boundaries are distinct, even planes, but they may be 

 rendered irregular by downward migration of coloring matter. 



Where alternations of light- and dark-red strata occur, the 

 more deeply colored beds are in most cases of finer grain than the 



