96 ANNALS NEW YORK ACADEMY OF SCIENCES 



enced by the supposed necessity of attributing the accumulation of all 

 sedimentary terranes to deposition in large bodies of water. The possi- 

 bilities of fluviatile accumulation on piedmont slopes or in depressed 

 basins were not recognized. Later studies of the eastern Trias, carried 

 out with this conception in mind, have shown that many strong arguments 

 may be advanced favoring this interpretation, and there is now a strong 

 tendency toward a general adoption of this point of view.^ To the writer, 

 the evidences in support of this view appear of great weight, and through- 

 out the present paper it is accepted without reservation. 



With this explanation, the conditions of Triassic deposition may be 

 summarized as follows : The processes of mountain-folding which 

 brought the Permian period to a close in eastern North America found 

 expression along lines approximately parallel to those which had charac- 

 terized previous periods of orogenic movement along the Atlantic border 

 and resulted in the uplift of the Appalachians along axes having in 

 general a northeasterly-southwesterly trend, but in places (as through 

 Pennsylvania) departing quite widely from the general course. As a 

 phenomenon which was probably closely associated with the structural 

 instability attendant upon this period of orogenic development, secondar}' 

 adjustments continued throughout a prolonged period.^ The most im- 

 portant later movements of this character, so far as their history may be 

 read, resulted in the formation of depressed areas closely parallel to the 

 axes of Appalachian folding but in general somewhat to the southeast- 

 ward of the main ridges. The downthrow or downwarping of these areas 

 does not seem to have been sufficient to bring the depressions beneath the 

 level of the sea, but, owing to their low-lying position, they formed, 

 during the Triassic, areas of rapid accumulation of sediments of conti- 

 nental type, brought in by torrential streams as a result of the waste of 

 the bordering uplands under climatic conditions of semi-aridity. 



There is some question as to the former extent of the areas on which 



1 For evidences "of sub-aerial accumulation see 



W. M. Davis : 18th Ann. Rept. U. S. Geol. Surv., pt. 2, p. 32, 1896-1897. 



J. V. Lewis : "The Origin and Relation of the Newarlj Rocks," Ann. Rept. State 

 Geol. N. J. for 1906, pp. 99-129. 



C. N. Fenner : "Features Indicative of Physiographic Conditions Prevailing at the 

 Time of the Trap Extrusions in New Jersey," Jour. Geol., vol. 16, pp. 229-327, 1908. 



a I. C. Russell : "The Newark System," Bull. 85, U. S. Geol. Surv., pp. 77 and 83, 

 1892. 



E. J. SCHMiTZ : "The Structure of the Richmond Coal-Basin," Trans. Am. Inst. Min. 

 Eng., vol. 24, pp. 397-408, 1894. 



J. V. Lewis : Op. cit., p. 107. 



O. J. Heinrich : "The Mesozoic Formation in Virginia," Trans. Am. Inst. Min. Eng., 

 vol. 6, p. 266, 1878. 



W. M. Davis : "The Triassic Formation of Connecticut," 18th Ann. Rept. U. S. Geol. 

 Surv., pt. 2, p. 35, 1896-1897. 



