202 Scientific Geology. 



strata, extending at least from Cape Cod to the borders of the Gulf of 

 Mexico ; and how far eastward where the Atlantic now rolls, we can 

 form no probable opinion : though there is some reason for supposing 

 that they once even reached Europe ; along whose shores similar 

 strata are found at present. As we proceed southward along the 

 coast from Martha's Vineyard, the plastic clay appears on Long Island, 

 in New Jersey, in Maryland, at Natches, at the Chicasaw Bluffs, &c ; 

 according to the statements of Mr. Finch.* If this should prove to 

 be one continuous formation, as there is some reason for supposing, it 

 will be by far the most extensive deposite of this kind hitherto dis- 

 covered. We do know that this and other tertiary formations, with 

 the ferruginous sand, which is the highest of the secondary rocks, 

 occupy nearly all that wide range of level country lying along the 

 Atlantic coast of the Southern States. 



Theoretical Considerations. 



It is universally agreed that all the tertiary formations have been 

 deposited from materials diffused or dissolved in water : and it is now 

 generally admitted that these deposites took place in independant ba- 

 sins and at various epochs. One of the most remarkable facts in re- 

 lation to these deposites, is the frequent alternation, or admixture, of 

 marine with fresh water or terrestrial relics. Thus, at Gay Head, we 

 have lignites and dicotyledonous vegetables mixed and probably alter- 

 nating with the remains of sharks, alcyonites, crabs, and marine shells. 

 In some instances, such facts may be explained by supposing alternate 

 elevations and depressions of the surface, so as to bring salt and fresh 

 water successively over these deposites. But more usually it is prob- 

 able these strata were deposited in estuaries, which were occasionally 

 inundated by fresh water : and as in early times the earth's surface 

 was perhaps, more level than at present, these inundations might be 

 more extensive than any that now occur. 



Another interesting fact, which has been recently established by 

 Beaumont, Desnoyers, Boue, and others, is, that during the period 

 in which these tertiary deposits were proceeding, violent convulsions, 

 succeeded by long intervals of repose, took place ; by which some of 

 the highest mountains on the globe were elevated, and portions of 

 these formations elevated along with them ; so as now to crown their 



* Am. Journal of Science Vol. 7. p. 34 : also Conrad's Fossil Shells Vol. 1. p. 14. 



