174 MARL FROM ASHLEY RIVER, S. C. 



The proportion of phosphate of lime is large, and may be 

 owing to the impalpable remains of animals that must have 

 frequented these early seas in myriads, or it may be peculiar to 

 the little shelly remains of polythalamia that form such a large 

 portion of this bed. The fluoride of calcium, which I believe 

 is here pointed out for the first time as existing in marls, does 

 not owe its origin to any spiculse of bony matter present in 

 the specimen examined, at least none that the microscope could 

 detect; so we must attribute it either to osseous matter tritu- 

 rated to an impalpable powder, or, what is more probable, sup- 

 pose that it forms a part of the calcareous covering of those 

 animalculse just alluded to, the remains of which form the 

 foundation of the city of Charleston. The ammonia is held 

 mechanically in the pores, associated perhaps with carbonic 

 acid, and is easily rendered apparent by dropping caustic 

 potash on the marl. This has been found present in all the 

 marls I have examined, and the fluoride of calcium in several. 



