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 witli acids, con- 

 tain but five per cent of lime. 



Again, we find large beds of calcareous marl, containing at least 

 thirty seven per cent of lime, the remainder being silex, iron, Sac. 

 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 in 

 profusion : chert, (in the calcareous beds) amber, retinasphalt, lig- 

 nite, and small spherical masses of a dark green color and compact 

 texture, apparendy analogous to those found in the green sand of 

 France.* Mr. Hayden suggests to me that these may be the Dis- 

 colites of the Abbe 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. 



* Cuv. and Biong. Desc, Geol. des Euv. de Paris, p. 16, &,c. 



