9. 



site of a large Triassic basin, and under the Bay of Fundy and along its 

 east shore in Nova Scotia another such basin exists. See Plate 9. 



The Triassic areas are generally sites of lowlands because the basin 

 beds have yielded to erosion more than the adjacent crystallines. The 

 Triassic lowlands is the physiographic name generally given to the Penn- 

 sylvania-New Jersey basin. The lowlands are marked, however, by ridges 

 of trap rock that stand rather prominently above the lowland plain. 



EASTERN TRIASSIC BASINS 



DISTRIBUTION OF BASINS 



A series of long, narrow basins of Triassic deposits occurs along the 

 eastern margin of the continent. It will be seen by reference to the Geo- 

 logic Map of the United States or Geologic Map of North America that 

 the basins start at the north boundary of South Carolina in the Piedmont 

 crystalline province and extend through North Carolina, Virginia, Mary- 

 land, Pennsylvania, and New Jersey to the lower Hudson River Valley in 

 New York. The basin in Pennsylvania and New Jersey is the largest of any 

 in the United States, and for a distance between the Carlisle prong and 

 Reading prong of the Blue Ridge element, it borders on the Ridge and 

 Valley province. 



The Connecticut River Valley in Connecticut and Massachusetts is the 



NATURE OF TRIASSIC ROCKS 



General Character 



The Triassic sedimentary rocks of the eastern basins are chiefly clastic 

 and dominantly red. Fanglomerates, conglomerates, sandstones, arkoses, 

 siltstones, shales, and argillites are the common sedimentary types. Much 

 basic magma has invaded the sediments and now exists as thick sills and 

 long dikes of diabase. Basalt flows from the same magma are also inter- 

 calated in the shales and sandstones. The intrusive rocks have commonly 

 altered the red sediments to blue or gray along the contacts in zones 50 

 to several hundred feet thick. 



New Jersey-Pennsylvania-Maryland-Virgina Basin 



Newark Group. The sediments of the New Jersey-Pennsylvania-Mary- 

 land-Virginia basin are known as the Newark group. The basin has a 

 maximum width of 30 miles and is over 300 miles long. Part of it is shown 

 in Fig. 9.1. The Newark group has been classified in three formations, the 

 Stockton, Lockatong, and Brunswick, the last-named being the youngest. 

 These subdivisions are clearly separable along the Delaware River and 

 northeastward in New Jersey, where they were first established and 

 named. 



The Stockton formation in general comprises arkosic sandstone with 

 some red-brown sandstone and red shale, in irregular succession and pre- 

 senting many local variations in stratigraphy. It lies unconformably on 

 Paleozoic and pre-Paleozoic crystalline rocks. The sandstones are in places 

 cross-bedded, and the finer-grained rocks exhibit ripple marks, mud 

 cracks, and raindrop impressions, which indicate shallow-water conditions 



128 



