278 Organic Remains of the Ferruginous 
sometimes this clay is mixed with the marl, forming the marly clay 
of Mr. Peirce ; in other instances the two are seen in alternate layers. 
Again, the marl is seen of a yellowish brown color, friable, or com- 
pact, and filled with green specks of the silicate of iron. Some of 
the greenish varieties are also very compact, rendering it extremely 
difficult to separate the fossils from their matrix. The friable blue 
marls often contain a large proportion of mica in minute scales. 
Other localities present beds of siliceous gravel, (turtia? of the 
French) the pebbles varying from the size of coarse sand to one and 
two inches in diameter. These are cemented together by oxide and 
phosphate of iron, and contain the same fossils as the earths already 
described. ‘The most striking instance of this kind is at Mullica 
Hill, in New Jersey. Similar mineralogical appearances, but without 
fossils, occur in the lower beds at the Chesapeake and Delaware ca- 
nal. At the latter place we also find a friable siliceous sand, of a 
bright green color, answering to the glauconie sableuse of Brongniart: 
also a fine, pure white sand, with abundance of lignite ; and exten- 
sive beds of brown and yellow ferruginous sands, more or less argil- 
laceous. 
Some of the blue marls which effervesce strongly with acids, con- 
tain but five per cent of lime. 
Again, we find large beds of calcareous marl, containing at least 
irty seven per cent of lime, the remainder being silex, iron, &c- 
Also a hard, well characterized, subcrystalline limestone, filled with 
zoophytes. 
All these diversified appearances pass by insensible degrees into 
each other, exhibiting an almost endless variety of mineralogical char- 
acters. 
The mineral substances found in these beds are, iron pyrites m 
profusion: chert, (in the calcareous beds) amber, retinasphalt, lig- 
nite, and small spherical masses of a dark green color and compact 
texture, apparently analogous to those found in the green sand of 
France.* . Hayden suggests to me that these may be the Dis- 
colites of the Abbé Fortis. Their structure, however, does not ap- 
pear to be organic, although they often have a shark’s tooth, or a small 
shell, for a nucleus. Larger spherical bodies also occur, resembling 
the nodules of clay iron stone, so common in some parts of England. 
Saceae Sei Ce a 
__ * Cuv. and Brong. Desc, Geol. des Env. de Paris, p. 16, &c. 
