264 GREEN SAND AND CRETACEOUS. 
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- 
Jersey, it is very doubtful whether it ought to be 
classed in this formation. At any rate, it will prove 
of little value, if, as Prof. Rogers supposes, the fer- 
tihzing 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 shown 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 sand 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* 
