682 



GEOLOGY 



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 Virginia-New York 

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

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

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

 this with that of Acadia, and that the separation was effected by 

 erosion; but this suggestion does not seem well founded. 1 



Fig. 465. Diagram showing the development of a trough, now partly filled 

 by sediment, by warping. 



Fig. 466. Diagram showing the development of a trough by faulting. 



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 are extrusive, having been 

 poured out on the surface of the inferior beds and subsequently 

 covered by sediment; others are intrusive (sills), having been forced 

 in between the layers of sedimentary rocks after the latter were 

 deposited. 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. 



1 For summary of the Trias of Connecticut, see Davis, 7th Aim. Hrpf .. 

 U. S. Geol. Surv., or a fuller and later account in the Isth Ann. Kept., Pt . II 

 See also the Holyoke folio, U. S. Geol. Surv., ami for the Pompcr-aui; area. 

 Hobbs, 21st Ann. Kept., U. S. Geol. Surv., Pt. III. 



