8 GEOLOGY. 



deposited, seems certain. The depressions may have born due to 

 warping or to faulting, or partly to the one and partly to the other 



Fig. 312. — Diagram showing the development of a trough, now partly filled by- 

 sediment, by warping. 



(Figs. 312 and 313), and their development may have continued as 

 deposition proceeded. Some of them may have been the sites of broad 

 river valleys/ which, in the general uneasiness which marked the close 

 of the Paleozoic era, were brought into such an attitude as to become 

 sites of deposition. It is to be noted that deposits of the type repre- 

 sented by the Newark series imply warping, rather than depression. 



Fig. 313. — Diagram showing the development of a trough, by faulting. 



The warping may have been the uplift of the surroundings of the areas 

 of deposition, rather than the depression of those areas ; or it may have 

 involved the depression of the areas of deposition as well as the uplift 

 of their surroundings. The deposits now making in the Great Basin 

 afford some analogy. However formed, the depressions (relative) in 

 the surface of the present Piedmont region became the sites of lakes, 

 bays, estuaries, dry basins, or of aggrading rivers. Lacustrine ; estua- 

 rine, and fluviatile conditions may have alternated from time to time 

 in the various troughs where sedimentation was in progress, and the 

 sea may have gained access to some of them from time to time. 



Since the Trias of the Connecticut valley and of the areas south 

 and west of the Delaware are bordered on either side by older ter- 

 ranes, it is easy to see how the areas of deposition might have been 

 enclosed. But from the Hudson to the Delaware the series is bordered 



x Shaler and Woodworth, 19th Ann. Rept. U. S. Geol. Surv., Pt. II, pp. 399-407. 



