GREEN SAND AND CRETACEOUS. 



N. 



Green sand has lately been found by Professor 

 Hitchcock in Marshfield, Massachusetts, and he 

 thinks it abounds in Barnstable and Plymouth coun- 

 ties ; but as it occurs among primitive rocks, and, 

 besides, contains no potash in its composition, which 

 is a constant ingredient in the green sand of New- 

 JersSy, it is very doubtful w^hether it ought to be 

 classed in this formation. At any rate, it will prove 

 of little value, if, as Prof. Rogers supposes, the fer- 

 tilizing properties of this mineral are owing to the 

 potash contained in it. That such is the fact there 

 can be no doubt whatever. 



The character of its fossils, as well as its mineral 

 contents, proves that the secondary cretaceous for- 

 mation has been deposited upon the bed of the ocean 

 in places where the sea encompassing the coast was 

 shallow^ like that which now exists over the wide 

 belt of shoals and soundings in front of our Atlantic 

 coast. This is shov^^n by the habits of the animals 

 whose remains are found, and the tokens of land, 

 derived from the coarseness of the sands, as well as 

 the remains of terrestrial vegetation. Prof. Rogers 

 considers the green «and as a chemical precipitate, 

 thrown down from solution in the waters of that 

 ancient sea, and not a sediment of sand mechanical- 

 ly carried out from land, as must have been the case 

 with the silicious sands adjacent to it. And here 

 is an important problem for the chemist : required 

 the conditions necessary to precipitate such a de- 

 posite in comparatively so short a space of time. 



The rocks which we have thus attempted briefly 

 to describe in this and the last chapter, constitute 

 the great secondary formation of the United States, 

 which is bounded by the irregular border of the 

 transition series already described, extending from 

 between the Alabama and Tombigbee rivers to Fort 

 Ann, near Lake Champlain. On the northwest it 

 follows the shores of the great lakes, and loses it- 

 self in the alluvial of the great basin of the Missis- . 



