1913.1 



NATURAL SCIENCES OF PHILADELPHIA. 



115 



ware River, gradually thinning westward, and dying out in northern 

 Chester County, but reappearing north of Lancaster and repre- 

 sented by 1,000 feet of carbonaceous sandstones at the Susquehanna; 

 and the Brunswick red shale and conglomerate, up to 16,000 feet 

 thick, which lies against the older rocks along the northern bound- 

 ary. Although the evidence is not sufficient for definite correlation, 

 it seems probable that these are roughly equivalent to the Bunter, 

 Lower Keuper, and Upper Keuper of Europe, respectively. 



The following sections represent two alternative explanations 

 of the structure of the Triassic basin in this region. 



GENERALIZED STRUCTURE SECTIONS of the TRIAS glC in 

 N PENNSYLVANIA Scale: l,nc/i= 6m,le? 



+- ^ ^ Pre -Trial. 



il-l^^^-t^t-tv'/ 



Section A. Assamir^ A fault Ai The Norfhern Bewndory. 





FVe-Tnassio 



Section B. As-JMinin^ Overlap At The Northern Boundor\^- 



It is believed that Section B most correctly depicts the relation- 

 ships existing through the greater part of the Pennsylvania Triassic 

 area, although in Connecticut and in northern New Jersey sections 

 of the type of A have been thought to accord best with the observed 

 facts. This conclusion is based, first, on studies of the actual 

 contacts exposed along the northern boundary and, second, on 

 certain inferences drawn from features shown by the rocks in other 

 portions of the area. 



While the northern boundary of the Triassic against the older 

 rocks is usually marked by a slight depression and deeply covered 

 by soil, more or less definite contacts can be seen in at least six 

 places, namely, Monroe on the Delaware; Springtown, Bucks 



