114 PROCEEDINGS OF THE ACADEMY OF [March, 



NORTH BORDER RELATIONS OF THE TRIASSIC IN PENNSYLVANIA. 

 BY EDGAR T. WHERRY, PH.D. 



The uniform gentle northwest dip of the Triassic Red-beds 

 throughout the greater part of the belt crossing southeastern 

 Pennsylvania has been a subject of comment since the earliest days 

 of study of the region. Henry D. Rogers, in his final report,^ 

 cleverly suggested that it was due to inclined deposition, from 

 northward-flowing waters, such as can be observed in present-day 

 river deltas. The inadequacy of this explanation is made apparent, 

 however, by the evident level-surface origin of the fossil footprints 

 and rain-drop impressions which have since been found, as well 

 as by the fact that in certain places, especially toward the northwest 

 border of the belt, the dips show considerable variations, both in 

 amount and direction. 



No simple process of uplift and folding, however, can account 

 for the relations observed. The fact that thousands of feet of 

 strata exposed in the southern portion of this belt are totally lacking 

 along its northern edge implies that either profound faulting must 

 have occurred there or that progressive overlap on an extensive 

 scale must have accompanied the deposition of the beds. In 

 the course of the writer's studies of the Triassic, carried on at 

 intervals during the past six years, some evidence bearing on this 

 point has been accumulated.- 



As shown elsewhere,^ the Triassic of Pennsylvania can be divided 

 into three formations, which from the base upwards are: the 

 Stockton (Norristown) arkosic sandstone and conglomerate, 5,500 

 feet in maximum thickness, which outcrops along the southern 

 edge of the belt; the Lockatong (Gwynedd) dark shale, which ap- 

 pears as a lens between the other two, 3,500 feet thick at the Dela- 



1 Geology of Pennsylvania, II, p. 814, 18.58. 



- This was presented in abstract at the meeting of the Geological Society 

 of America, December 29, 1911 {Bull. Geol. Soc. Amer., XXIII, 745), and at the 

 meeting of the Academy in conjunction with the Mineralogical and Geological 

 Section, May 21, 1912 {Proceedings, 1912, p. 156), but is now for the first time 

 published in full. 



3 Age and Correlation of the '"New Red" or Newark Group in Pennsvlvania, 

 Proc. Acad. Nat. Sci. Phila., 1912, pp. 373-379. 



