NORTH-CAROLINA GEOLOGICAL SURVEY. 89 



climate, that they became extinct at an earlier period than at 

 points farther south, and that the same species which were 

 once common on the coast of Virginia and Maryland, and 

 which are now extinct so far as that part of our coast is con 

 cerned, still live farther south where the climate is congenial 

 *o the species. 



CHAPTER VII. 



FERTILIZERS CONTINUED. 



Marl, its economical value. Composition of the Green Sand of the 

 Cape Fear River. 



61. The marls of North-Carolina do not rank so high as 

 the strong marls of other States. This is in consequence of 

 the large proportion of sand with which they are intermixed. 

 It appears that the coast has been from time immemorial the 

 great depository of sand. The rivers from the interior carry 

 sand or matter in which silex greatly predominates. The 

 rocks in the interior belong to the silicious class. Limestones 

 are absent. But the great amount of sand of the coast has 

 been probably derived from more distant sources, and hence 

 it is probable we must look to the regular currents of the 

 ocean which flow in, more or less, upon it, for the determa- 

 tion of the source from which its sands have been derived. 

 When the Atlantic tide reached inland as far as the last of 

 the series of falls of the rivers of the State, as the Roanoke, 

 Cape Fear and Nense, it acted upon a granite rock which 

 readily decomposed, and which must have furnished an im 

 mense quantity of silicious debris. This rock may, therefore, 

 have been one of the sources of the sand alluded to. Some 

 beds of marl are consolidated into rock, and where this con- 



