REPORT ON THE GEOLOGY OF NORTH AMERICA. 7 



of the United States, and to the southern part of the great cen- 

 tral valley, or basin of the Mississippi. The lines along which 

 these formations have been traced in the valley of the west are 

 few and far apart, so that our present survey is chiefly confined 

 to the tide-water plain along the Atlantic. 



The same line, which was before sketched as forming the 

 boundary of the Atlantic plain, will be observed, in tracing it 

 through the states of New Jersey, Pennsylvania, Delawai-e, 

 Maryland, Virginia, and North and South Carolina, to coincide 

 almost exactly with the western limit of the tertiary and se- 

 condary formations here to be discussed. From Long Island, 

 south, this barrier of primary rocks presents everywhere a re- 

 markably abrupt and well defined line of separation between 

 these newer deposits and the rocks of older origin. North of 

 Long Island, on the main land of Connecticut, Rhode Island, 

 and Massachusetts, the precise position of this line is not so 

 readily traceable. Along the coast of the two first states little 

 or nothing of the newer formations is seen; and, if we except 

 the small portions stated by Hitchcock as occurring in the valley 

 of the Connecticut river, and on the eastern peninsula of Mas- 

 sachusetts near Cape Cod, they have not been noticed on the 

 continent east of New York. The islands of Nantucket, Mar- 

 tha's Vineyard, and Long Island are all, however, embraced 

 within the area of the upper strata about to be described. 



The acknowledged difficulty of defining the exact sera to 

 which the newest deposits belong, is sensibly felt in treating 

 of those of the United States. The amount of strata within 

 this area which have had their origin in the class of geological 

 causes at present in action, is, no doubt, very considerable. 

 Indeed, geologists are accustomed to allude to the changes 

 wrought by the Mississippi and Niagara as among the most 

 striking within the recent period anywhere to be met with. 

 Nevertheless, it seems very possible that a large portion of the 

 alluvial matter which borders the mouths of the rivers and 

 coast, may have been formed before the earth, or this conti- 

 nent at least, was tenanted by man. The evidence upon this 

 point will be given present'y. The first class of phaenomena to 

 be examined are those which are unquestionably recent. 



Of volcanic action we have no traces east of the Mississippi. 

 The earthquakes which convulse the equatorial and southern 

 sections of the continent rarely reach the United States ; and 

 when felt, they come with such greatly diminished force as to 

 be hardly sensible. The forces now in action are, therefore, 

 exclusively aqueous. These, however, prevail over very exten- 

 sive areas, as will be seen on adverting to the size and num- 



