292 STUDIES FOR STUDENTS 



inclusion of conglomerates whose component pebbles frequently con- 

 sist of fresh blocks of granite, pegmatite, and other rocks subject to 

 decay, testifying to a partial dominance of disintegration over decom- 

 positioa; by such an example as the Mauch Chunk red shales and 

 sandstones, 3,000 feet in maximum thickness, following immediately 

 upon the gray Pocono sandstone and its gradual transition above into 

 Pottsville conglomerate, red shales alternating with conglomerate 

 horizons. 



That conditions of deposition permitting oxidation had much to do 

 with the development of red in the consolidated sediment is indicated 

 by the usual poverty in fossils, especially in those of marine origin; 

 by the repeated intercalation in the Basin of Sistan of pink to brown 

 silts, regarded by Huntington as having been deposited subaerially, 

 with green clays, considered with good evidence as typically lacus- 

 trine.^ As a further illustration, the Wamsutta red-beds of the Car- 

 boniferous of the Narragansett basin are regarded by Woodworth 

 as represented south of Providence by the lower strata of the Kings- 

 town coal-bearing series. In the vicinity of Pawtucket the coal- 

 measures underlie the Wamsutta, though somewhat farther north 

 the latter are only separated from the granite by the basal arkose beds 

 of the Pondville group. ^ Woodworth states that the coloring of the 

 Wamsutta red-beds appears to have taken place before transportation. 

 This view, however, leads to difficulties which he states on the same 

 page. All difficulties, seem, however, to be avoided if it be considered 

 that the red is the result of dehydration during^consolidation and that 

 these beds retained their iron because they were deposited in an upper 

 and better-drained portion of the basin under a climate which per- 

 mitted for a time their seasonal drying. 



Turning to the climatic significance of red, it would therefore 

 appear both from theoretical considerations and geological observa- 

 tions that the chief condition for the formation of red shales and 

 sandstones is merely the alternation of seasons of warmth and dryness 

 with seasons of flood, by means of which hydration, but especially 



1 The Basin 0} Eastern Persia and Sistan, "Carnegie Institution Publications," 

 N0.I26, 1905, p. 287. 



2 "Geology of the Narragansett Basin," Monograph XXXIII, U. S. Geological 

 Survey, 1899, pp. 134, 141. 



