REPORT ON THE GEOLOGY OF NORTH AMERICA. 11 



rock — no relics of such barriers being seen, for example, among 

 the horizontal formations of the Atlantic plain — is, I think, 

 conclusive evidence that we must seek for some other cause. 



That the cause which has given the delta of the Mississippi 

 its present elevation was the uplifting agency of forces from 

 within the earth, we shall see additional evidence for admitting, 

 when I treat presently of some of the newest of our fossilifer- 

 ous deposits. In the present infancy of geological research in 

 the United States, we are not prepared to venture any views 

 upon the age to which the terraces in question belong. It is 

 very possible that they may be finally referred to several distinct 

 periods. Many of them are covered by the general capping of 

 diluvium, which I'enders it very likely that the date of some 

 of them is earUer than the recent period. In the absence of 

 organic remains, it is wisest to leave the discussion of the age 

 of these formations open until a larger stock of information has 

 been gathered concerning them. 



Of the Coast Islands, and their probable Origin. — Having, 

 in the previous section, given some account of a few of the 

 causes now in action on this continent, as a specimen of the 

 kind of phsenomena which in this country present themselves on 

 a scale of peculiar magnitude, I sliall proceed to a feature in 

 our geology closely connected vidth the foregoing class of opera- 

 tions, implying the agency of almost the very same powers, 

 and, if I mistake not, taking us into a period very little, if at 

 all, earlier than that of the river deltas and alluvium just de- 

 scribed. There is to be seen lying a little off from the main 

 shore, along the chief extent of the Atlantic coast, an interesting 

 range of shoals and islands, all running parallel with the shore, 

 and distinguished by the same uniform features. These long, 

 narrow, and low islands of sand range from Long Island to 

 Florida, and around nearly the whole northern sweep of the 

 Gulf of Mexico. They are rarely more than a mile or two 

 wide, sometimes 20 or 30 miles long, and, on an average, 

 about 12 feet high. The geology of Anastasia Island, on the 

 coast of Florida, is a representation of many others, though it 

 must be confessed we know extremely little respecting them. 



Anastasia Island, opposite St. Augustine, upon the eastei-n 

 coast of Florida, is, according to Mr. Dietz (Jour, of the Acad, 

 of Nat. Sci. Philadelphia), about 10 or 12 miles long, l-^ broad, 

 and has not more than 10 or 12 feet of elevation above the level 

 of the ocean. It lies parallel to the shore, at a distance of from 

 2 to 3 miles. The greater part of the northern portion, and 

 perhaps the whole of the island, is composed of horizontal 

 layers of a semi-indurated rock, consisting wholly of fragments 



