FORMATIONS AND PHYSICAL HISTORY 



487 



with their decisive evidences of shallow-water or subaerial origin, 

 siuh us ripple-marks, sun-cracks, tracks of land animals, etc., 

 idicate either that the sediments were deposited in an inclined 

 >sition, or that subsidence accompanied the deposition. For the 



Fig. 414. Diagram showing the development of a trough by faulting. 



adequate supply of sediment, it would seem that the lands border- 

 ing the areas of deposition were raised, relatively, as the troughs 

 \\i-re filled. 



Former extent. It is possible, and perhaps probable, that the 

 areas of the Newark series from Virginia to South Carolina were 

 once connected with one another, and with the Pennsylvania-New 

 York area, though such connection has not been demonstrated. It 

 has even been suggested that the Newark of the New York-Virginia 

 areas was once connected with that of the Connecticut valley, and 

 this with that of Acadia, the separation being effected by erosion; 

 but this suggestion does not seem well founded. 1 



Igneous rocks. Igneous rocks are associated with the sedi- 

 mentary beds in dikes, and in sheets interbedded with the shales 

 and sandstones. Some of the sheets were extruded and subse- 

 quently covered by sediment; others were intruded (sills) between 

 the layers of sedimentary rocks. Certain isolated bodies of igneous 

 rock may represent volcanic plugs. The sheets of igneous rock 

 (usually called trap, though largely basalt) vary in thickness from 

 a few feet to several hundred. 



Structure and thickness. The structure of the Newark series 

 is generally monoclinal. In the Connecticut Valley the dip is about 

 20 (10 to 25) to the eastward. In the New York- Virginia area 2 

 it is io-i5 to the northwest. The strata are otherwise somewhat 

 deformed, though never closely folded. The series is faulted ex- 

 tensively. On account of the faulting, the thickness of the series 



1 For summary of the Trias of Connecticut, see Davis, i8th Ann. Rept., U. S. 

 Geol. Surv., Pt. II. 



2 For summary of the Newark of New York and New Jersey, see Kurnmel, 

 Rept. of the State Geologist of New Jersey, 1896, and Jour. Geol., Vol. VII. 



