222 
PRIMARY ROCKS. 
Trenton. From that point they extend south, form- 
ing the eastern boundary of the primary area above 
rAentioned. 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 chffs. From this ocean boundary all the 
region embracing the New-England States, and the 
