13 



New Jersey, south-east of Salem, and continues through all the 

 States south of this, forming their Atlantic margins, and extend- 

 ing from one hundred to one hundred and fifty miles west from 

 the sea. 



MIDDLE TERTIARY FORMATION. 



SVN. London (/lay of English author*; Calcairo grassier of the French. 



Mineralogical characters. This formation, like most others, 

 presents itself under various Mineralogical appearances ; it 

 often exhibits beds of silicious sand, of a brownish colour, and 

 in this the fossils are in the finest preservation. Another variety 

 is a friable granular limestone, containing comminuted frag- 

 ments of shells, and indeed is sometimes almost wholly com- 

 posed of them. It is of a light ferruginous colour, and strongly 

 resembles certain varieties of the Calcaire grassier of France. 



Again, this formation presents a compact tenacious lime- 

 stone, with a dull granular fracture, and replete with minute 

 green grains. It contains a large proportion of clay, and though 

 abounding in fossils, these are mostly mere casts. 



Organic characters. "The testaceous mollusca are very nu- 

 merous and beautifully preserved, often retaining nearly the 

 appearance of recent shells. There are very few genera of recent 

 shells which have not some representation imbedded in this 

 formation, but the specific character is usually different, that 

 difference being often, however, so minute as to escape an un- 

 practised eye : on the other hand, but few of the extinct genera, 

 so common in the older formations, occur in this; so that it 

 seems to hold a middle character in this respect between the 

 earlier and more recent beds." 



Here again, the analogy which exists in the organic charac- 

 ters of this formation, on both sides of the Atlantic, is not less 

 marked than in the Upper Marine strata. 



The Calcaire grossier, of the French, is a coarse limestone, 

 more or less hard ; some of its beds are sandy and contain green 

 grains of silicate of iron. This division of the London Clay is 

 amazingly productive of organic remains ; and it will be here- 

 after shewn that some of its fossils are specifically the same 

 with those of the contemporaneous deposits of this country. 



Geographical distribution. In the vicinity of Fort Washing- 

 ton, on the Potomac river, Maryland, this formation first ap- 



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