THE TRIASSIC PERIOD. 17 



is to the east, while still another appears to represent the bottom of an 

 old syncline. There is, on the whole, less evidence of disturbance at 

 the close of the Triassic period in this latitude than farther north. 

 The faulting is less, though by no means absent, 1 and igneous rock 

 is less abundant or even wanting. The coal-beds, of considerable 

 thickness in this region, indicate conditions of stability during long 

 intervals of time. 2 



Thickness. — The thickness of the Newark series is variable and, 

 on account of the faulting, difficult of determination. In the Rich- 

 mond area of Virginia, the thickness is estimated at something more 

 than 3000 feet. In the areas farther south, the thickness is less, though 

 generally unmeasured. In New England, the thickness is estimated 



TUCKAHOE CREEK 



n 



Fig. 322. — Structure of the Newark series on the James River, Richmond area, Va. 

 A A, minor flexures; //, faults. Structure of the deeper parts hypothetical. The 

 heavy black band represen s coal. (Shaler and Woodworth, U. S. Geol. Surv.) 



at 7000 to 10,000 feet, and in New Jersey 12,000 to 15,000 feet. 

 Undiscovered faults may exist which, by repeating beds, have led to 

 exaggerated estimates. 



Correlation. — The structural relations of the Newark series in 

 the United States would not determine its age. The formations lie 

 unconformably on rock which is mainly pre-Cambrian, and they are 

 overlain unconformably by Cretaceous beds. About the Bay of 

 Fundy, however, the rocks lie unconformably on the Carboniferous 

 and early Permian. The physical relations of the Newark series there- 

 fore show that it is post-early-Permian, and pre-Cretaceous. Between 

 the Permian and the Cretaceous there are two periods, the Triassic and 

 the Jurassic. In the reference of the series to the former, the chief 

 reliance is usually placed on the fossils, and on the same basis the 

 series is believed to represent only the later part of the period. 



There is another reason for believing the Newark series to be older 



1 Keith, Harper's Ferry, Va.-Md.-W. Va. folio, U. S. Geol. Surv. 



2 Glenn, Am. Geol., Vol. XXIII, pp. 375-9. 



