222 



PRIMARY ROCKS. 



Trenton. From that point they extend south, form- 

 ing the eastern boundary of the primary area above 

 mentioned. The eastern line of this is marked by 

 the western limit of the tertiary and cretaceous rocks 

 of the Atlantic plain ; its western or northwestern 

 boundary is traced crossing the Delaware a mile 

 and a half above Trenton, and meeting the Schuyl- 

 kill about twelve miles from Philadelphia. As the 

 belt widens still to the northwest, the same line 

 passes more and more off from the coast, passing 

 the Potomac river twenty-two miles west of Wash- 

 ington, and merging into the previously traced belt 

 somewhere near the Rappahannock, in Virginia. 

 The separation of the primary into these two tracts 

 over so wide a space is owing to the position of 

 the very long belt of the red shale and sandstone 

 series, which, from the Rappahannock to the Hud- 

 son, ranges in a central direction between them. 

 An insolated group of the same rocks lie along the 

 Valley of the Connecticut, in a detatched basin in 

 the eastern section of Massachusetts, between Bos- 

 ton and Rhode Island, and also along the country 

 bordering the Hudson River, and Lakes George and 

 Champlain. 



The primary rocks, then, range in a continuous 

 belt through Virginia, North Carolina, South Caro- 

 lina, and Georgia, as far as the Alabama river in 

 Alabama, and occupy a breadth in most parts of this 

 course of from 80 to 100 miles, having for their 

 eastern boundary the horizontal strata of the Atlan- 

 tic plains, and for their western the great Appalach- 

 ian valley lying at the base of the Blue Ridge, and 

 the long range of mountains which stretch farther 

 to the southwest. Thus, from the coast of New- 

 Brunswick to the mouth of the Hudson, except the 

 Peninsula of Cape Cod, the sea washes against pri- 

 mary rocks, sometimes low, sometimes in bold pro- 

 jecting cliffs. From this ocean boundary all the 

 region embracing the New- England States, and the 



