10 CRETACEOUS GROUP 
of France.* They are one or two inches in diameter ; 
and although their structure is not organic, they often 
have a shark’s tooth or a shell, fora neucleus. Can they be 
Coprolites? Larger spheroidal bodies also occur, with 
fissures radiating from the centre, like those of the clay 
iron-stone so common in England. 
Lignite is extremely abundant: it is found in the lower 
strata of the Chesapeake and Delaware canal, in almost 
every variety, from charred wood to well characterized 
jet. Even the limbs and trunks of trees have been there 
found many feet in length, and perforated by the teredo.+ 
2. Calcareous strata. These consist of several va- 
rieties of carbonate of lime, of which the following are 
the most remarkable: 
An extremely friable mass, containing at least thirty- 
seven per cent. of lime, with a considerable proportion 
of iron, silex &c. It appears to be almost entirely 
composed of disintegrated zoophytes. 
A yellowish or straw colored limestone, as hard as the 
carboniferous varieties ; it contains numerous organic re- 
mains. 
A granular or subcrystalline limestone, intermediate in 
structure between the former two, and embracing similar 
fossils. 
*Cuv. and Brong. Desc. Geol. des env. de Paris, p. 16. 
+ Although I am satisfied that our cretaceous strata contain lignite, yet I by no 
means refer all our lignites to those strata. The deposits of this kind last men 
tioned, lie between the deep cut of the Chesapeake and Delaware canal and its 
western extremity, and probably belong to a much more recent period than the 
chalk series. This subject is now in the able hands of my friend Henry D. Ro- 
gers, Esq. 

