10 CRETACEOUS GROUP 



of France.* They are one or two inches m diameter ; 

 and although their structure is not organic, they often 

 have a shark's tooth or a shell, for a 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. f 



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. Gcol. des env. de Pari?, p. 16. 



t 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 

 tioncd, 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- 

 Efq 



