6 FOURTH REPORT 1834. 



Munford Falls on the Roanoke, the Neuse at Smithfield, Cape 

 Fear River at Aveiysboro, the Pedee near Rockingham, the 

 Wateree near Cambden, the Congaree at Columbia, the Falls at 

 the junction of the Saluda and Broad Rivers, the Savanna at Au- 

 gusta, the Oconee at Milledgeville, the Ockmulgee at Macon, 

 Flint River at Fort Lawrence, the Chattahooche at Fort Mit- 

 chell, &c., deviating thence north-west through the state of 

 Mississippi. Towards the southern termination of this rocky- 

 ledge, in Alabama for instance, it does not consist, as it generally 

 does elsewhere, of gneiss, but is formed of the ancient sandstone 

 and limestone of the Alleghanies. It every^vhere, however, ap- 

 pears as a natural line of division, of great length and vinifor- 

 mity, separating two tracts of very dissimilar geological age and 

 features. The upper tract, which I have called the Atlantic slope, 

 possesses a very variable width; it is narrow in New York and the 

 New England States, where the mountains approach the coast, 

 and narrow also in Alabama, where they approach the plains oc- 

 cupied by the cretaceous rocks of the south, but is much expanded 

 in Virginia and the Carolinas. Here it has a breadth of about 

 200 miles, ascending from the tide in an undulating hilly sur- 

 face, to a mean elevation of perhaps 500 or GOO feet near the 

 mountains. As it approaches these, its hills swell into bolder 

 dimensions until we gain the foot of the blue ridge or first chain 

 of the Alleghanies. It consists almost exclusively of the older 

 sedimentary and stratified primaiy rocks. This fine hill tract 

 exhibits a marked uniformity in the direction of its ridges and 

 valleys, running very generally north-west and south-east, or 

 parallel with the mountains. The ridges, though not high, are 

 long, and the fertile intervening valleys very extensive. It em- 

 braces a variety of fine soils, and an immense water power in its 

 rivers and running streams. 



Geology of the United States. — I propose to treat of our 

 formations in the order of the latest first, commencing the 

 survey of each group in the districts where it is best known. I 

 shall therefore, in this first part of my Report, describe whatever 

 is known of our recent, tertiary, and cretaceous formations, and 

 shall reserve an account of the rest of the secondary and all the 

 primary rocks for the next annual meeting of the Association. 

 By the delay I hope to be able to add materially to the accu- 

 racy of the geological map, and it will enable me to present 

 some of the results of the geological survej-s now set on foot by 

 the States of Maryland and Tenessee, together with whatever 

 else may in the mean while be brought to light. 



The tertiary and cretaceous groups yet known to us in North 

 America are confined almost exclusively to the Atlantic plain 



