the formation of Phosphate Nodules. 408 



The South Carolina phosphates are nodular in form and 

 found varying in size from that of a pea to nodular aggregates 

 weighing ten pounds and more. They all have smooth and 

 rounded surfaces as if water worn and vary greatly in shape. 

 The rock is found in beds varying from a few inches to one to 

 two feet in thickness, underlying from three to ten and more 

 feet of siliceous clay and overlying the calcareous marl of the 

 region. It contains from 50 to 65 per cent of normal calcium 

 phosphate ; and the marl lying directly under it contains from 20 

 to 30 per cent of the same salt, which amount rapidly decreases 

 at a depth of a few inches to 10 to 20 per cent and finally 

 reaches the usual amount found in the marls — 2 to 9 per cent.* 



This concentration of phosphate in the marl directly under- 

 lying the rock clearly indicates a gradual segregation from the 

 rock above. 



The rock on examination with the eye, with and without 

 the aid of the glass, is found to contain fossil shell forms and 

 casts similar to those found in the underlying marl, but in a 

 much better state of preservation and much harder in the 

 former than, the latter. 



I have found, in many instances, in the cavities which have 

 heen left by shells between the outer and inner casting, a 

 brownish white, very finely divided powder, which gave on 

 analysis 84 - 65 per cent calcium phosphate [Ca 3 (P0 4 ) 2 ], a small 

 quantity of silica, of fluorine, organic matter and the rest 

 calcium carbonate. This clearly shows the direct replacement 

 of the carbonate of the shell by phosphate. 



From the similarity in structure of the phosphates and the 

 marls, and their occurrence, it is clearly seen that the former 

 are the phosphatized product of the latter ; and the object of 

 my work has been to see how far swamp water could have 

 aided in bringing about this result. 



There has been considerable work done on the action of the 

 so-called humus acids (humus, crenic and apocrenic acid, etc.) 

 on the soilf and also on phosphates^ in the soil, and it was 

 my intention to study the action of these acids on the normal 

 phosphate of calcium both alone and in the presence of cal- 

 cium carbonate ; but owing to their uncertainty of composition, 

 the extreme difficulty of obtaining them in a pure condition, 

 and particularly their liability to undergo change in attempts 

 to isolate them, I decided to study their action in their native 

 condition, and under circumstances as nearly as possible like 

 those under which they act in nature. 



* C. U. Shepard. 



f A. A. Julien. Am. Association for Advancement of Science, Proceedings, 

 1889. 



\ J. M. Bemmellen, Landwirtschaftliche Versuch-Station, 35, 36. 



