REPORT ON THE GEOLOGY OF NORTH AMERICA. 1$ 



than one such up-heave of the continent during the tertiary- 

 period, may possibly be found hereafter, when the various sy- 

 stems of plains and terraces along the rivers and the coast shall 

 have been more investigated. 



There can be no doubt that most of the islands opposite the 

 coast of the Middle States, New Jersey for instance, are hourly 

 on the increase. They consist, like the opposite main shore, 

 of marsh as a substratum, which is seen to receive a covering 

 of sand blown in from the sea side whenever the tides and gales 

 are favourable. Thus, the side of these islands next the sea is 

 sandy and on the increase, while that adjacent to the continent 

 is marshy, and in many cases appears to be wearing down 

 under the action of the rapid current which sweeps through the 

 intervening sound or strait. As a proof of the daily growth of 

 some of these islands, or beaches, as they are called. Cranberry 

 Inlet is now closed up, though it still bears the name " Inlet," 

 as may be seen upon any map of the Jersey coast. 



It is impossible, therefore, to refer them all to the period 

 which produced Anastasia Island, and the islands and coast in 

 its neighbourhood, though, regarding the manner of their for- 

 mation, there can be no doubt that the same combination of 

 causes, winds and currents, operated in producing them all. 

 These causes, as I have already shown, are active, in the pre- 

 sent day, in effecting similar deposits along the delta of the 

 Mississippi ; nor do I perceive any good reason why we should 

 not admit the agency of the same in remote tertiary periods. 

 Our rivers, since the appearance of the carboniferous forma- 

 tions, at least, must have been always very large, and have 

 formed vast deposits of sediment in the sea ; and there is 

 every reason to suppose that the gulf-stream, which has evi- 

 dently much to do in shaping these deposits, has existed since 

 an early period of our coast formations. The true age of that 

 great ocean current can only be decided when we know more 

 thoroughly the geology of the isthmus separating North from 

 South America. In the mean time we may safely apply the 

 actions which are daily witnessed upon our coast, to forma- 

 tions so very little older, as that of Anastasia Island. 



Raised Estuary Formations ofHhe Gulf of Mexico. — A 

 very extensive bed of shells, bordering on the Gulf of Mexico, 

 seems to claim a position somewhere in the group of formations 

 now before us. It appears to hold a place on the confines, as 

 it were, of the tertiary and the recent formations. It is thus 

 described by Mr. Conrad : " An interesting deposit borders the 

 Gulf of Mexico, and is probably several hundred miles in ex- 

 tent. It consists entirely of two species of shells, Cyrena Ca~ 



