Fig. 1. — Generalized geological map and typical cross-sections of the region within a radius of 



300 miles of New York City 



The oldest rocks of the region are those comprised in the crystalline areas of the Adirondacks, 

 New England, and the Blue Ridge and Piedmont portions of the Older Appalachians. These three 

 areas may be roughly pictured as an oldland enclosing an inland sea or depression on the west where 

 the Cambric, Ordovicic, Siluric, Devonic, and Carboniferous sedimentary deposits were laid down. 

 The Cambric and Ordovicic formations are essentially limestones and shales, not resistant to erosion, 

 which accounts for the persistence of the present Great Appalachian Valley along the western flank 

 of the oldland. 



After the deposition of the Siluric, Devonic, and Carboniferous beds there occurred the compres- 

 sion of the region which produced a general folding of the sedimentary beds next to the oldland where 

 the Appalachian ridges and valleys appeared. Further west there was no disturbance, the horizontal 

 bedding is preserved and the region is characterized as a plateau. 



During a later period (the Triassic) certain regions in the original oldland became covered with 

 red sand deposits interbedded with extensive lava flows, and portions of these areas were preserved 

 from later denudation by being downfaulted into the crystallines. They now constitute the Conneeti- 

 cut Valley and the Triassic Lowland. 



The latest geological formations are those comprising the present coastal plain on the eastern 

 side oC the oldland mass. 



