250 The Physical History of the Trias 



that, including all the rocks from the old red sandstone 

 upwards, 9,000 feet is not the greatest vertical denudation 

 which these rocks have suffered." 



Examples like these, illustrating the tremendous waste 

 which has affected nearly every portion of the earth exposed 

 to atmospheric agencies, might be multiplied without limit. 

 "We only give those noticed above, in order to show that an 

 immense denudation of the Triassic rocks of New Jersey and 

 New England, is a necessary result of their upheaval. 



We have, moreover, in the vast amount of material compos- 

 mo- the Triassic beds themselves, another striking example of 

 the extent of denudation. These strata, as we have seen, cover 

 thousands of square miles over, our country, and are many- 

 thousand feet in thickness, yet in the language of geology, 

 they are derivative rocks, and owe their accumulation to the 

 wear of pre-existing formations. To find the source from 

 which this material was derived, it is only necessary to notice 

 the region from which the Triassic estuary received the drain- 

 age. The country surrounding the Triassic area, on nearly all 

 sides, is formed of granitic rocks, which, as is well known, are 

 composed of the minerals quartz, felspar, and mica. The disin- 

 tegration of this material furnished an abundance of quartz 

 sand and mica, while the felspar sometimes appears as angular 

 fragments, but is usually decomposed and affords the more 

 earthy material of the shales. All these products of the disin- 

 tegration of the land, upon being delivered to the estuary 

 waters, would be rapidly assorted ; the coarser material would 

 be left near the shore, and the rest carried out by the current 

 and deposited at various points, determined by its specific 

 gravity, the strength of the currents, etc. We can also trace 

 the large amount of iron which colors the greater portion of 

 the Triassic beds, to the same source. Prof. A. A. Julien has 

 shown, by a microscopical examination of the Triassic sandstones, 

 that the iron which they contain was mainly derived from the 

 decomposition of the hornblende and chlorite so abundant in 

 the band of crystalline rocks surrounding the Triassic areas of 

 New Jersey and the Connecticut Valley. This region is also 



