5i° 



HISTORICAL GEOLOGY 



not derived from sedimentary rocks, as would have been the case if 

 the Appalachians had drained eastward through them, but are gra- 

 nitic and were derived from metamorphic and igneous rocks. The 

 present thickness of these deposits is very great, it being estimated 

 that some of those of Pennsylvania and Connecticut are several thou- 

 sand feet thick. The liability to error in estimating the thickness of 



Fig. 482. — Section across the Connecticut valley, showing the thick strata of sand- 

 stone (dotted) and the lava beds (solid black). The dotted line shows the present 

 outline of the surface. The complex structure of the underlying rock and the rock of 

 the highlands is well shown. (After Barrell.) 



these deposits, because of the concealed faults, is so great that no fig- 

 ures can be considered more than provisional. The sediments north 

 of Virginia are usually red sandstones and shales, with occasional 

 thin beds of black shale and limestone. 



In Virginia and North Carolina coal conditions prevailed, but, 

 with the exception of these and the abundant footprints of the Con- 

 necticut valley, fossils are rare. Fish and plant remains in thin beds 



Fig. 483. — Section across the Connecticut valley, showing the same region as in 

 Fig. 482 after faulting had occurred, and after erosion had worn the region to a pene- 

 plain. (After Barrell.) 



are, however, occasionally found. Since no marine fossils have been 

 discovered in any of the Triassic deposits of the east, the exact age 

 of these deposits is somewhat in doubt, but the evidence points to 

 the Upper Triassic as the time at which they were laid down. This 

 formation is known as the Newark because of its development near 

 the city of that name in New Jersey. 



During the deposition of these sediments lava flows of considerable 



