﻿Dr. J. L. Smith on Oxide of Cobalt from Silver Bluff. 103 



Organic remains are quite abundant in this marl, although in 

 an imperfect state. Its composition is somewhat peculiar, and a 

 knowledge of it may be of some general importance ; it varies 

 in the proportion of its ingredients, but seems to be constant as 

 regards their character. From among several analyses the fol- 

 lowing is selected as being an average one. 



Carbonate of lime, . 65-8 



Carbonate of magnesia, . . . 24 



15-6 

 100 



1-2 



Silica, 

 Alumina, 



Phosphate of lime, with a small quantity of 

 phosphate of magnesia, . . . 5*9 



Phosphate of iron, 



Fluoride of calcium, 



Crenate of iron, 



Crenate of lime, 



Ammonia, 



Organic matter, 



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

 ing to the impalpable remains of animals that must have fre- 

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

 little shelly remains of Polythalamia that form such a large por- 

 tion 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 spiculae of bony matter present in the spe- 

 cimen examined, at least none that the microscope could detect, 

 so we must attribute it either to osseous matter triturated to an 

 impalpable powder, or what is more probable, suppose 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 ap- 

 parent 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. 



IY. Oxide of Cobalt from Silver Bluff, South Carolina. 



The existence of this oxide was first brought to my notice by 

 Prof. Ellet ; it is accompanied by the oxide of manganese, and 

 with it stains a coarse gravel found in the primitive region of 



