NORTH-CAROLINA GEOLOGICAL SURVEY. 9 



to be replaced by soda, which no doubt takes the place of 

 potash in many vegetables where ash is rich in the alkalies. 



65. The sand of the marl beds of New Jersey varies from 

 39 to 70 per cent. ; the remainder of which is more or less 

 valuable in agriculture. 



The phosphate of lime is probably the most variable in its 

 quantity of all the valuable elements, and it is regarded as a 

 mixture, and not forming a chemical union with either of its 

 elements. Indeed it may in many specimens be seen and 

 distinguished by its greenish gray color. 



But it is never evenly distributed through the bed, as it has 

 been ascertained by analysis, that it has occasionally accumu 

 lated in the inside of shells. It is, however, always present 

 in the marl, and it no doubt exerts a favorable influence upon 

 vegetables. 



The upper bed at Blackrock differs in composition from 

 the lower. It is less gritty to the touch, is of a darker green, 

 more compact, and resembles a dark green clay. The sand 

 in it is greater in quantity than in the lower, but is much liner. 



On submitting it to analysis I found : 



Sand or silex, ^. . 93.43 



Peroxide of iron and alumina, 9.00 



Carbonate of lime, 1 1 .40 



Magnesia, 0.20 



Potash, 0.38 



Soda, 0.4-2 



Organic matter, 4.80 



Water, 3.80 



100.43 



The specimen submitted to analysis was taken near the 

 upper part of the bed, about four feet above the line, along 

 which the exogyra are the most numerous. 



The results which I have finally obtained by the analysis 

 of the green sand at Blackrock have disappointed me. I 

 expected at least twice as much potash as I have been able 

 to obtain ; still when the green sand is carefully examined 

 under the microscope it shows such a large intermixture of 

 sand, and such imperfect green grains of the silicates, that 



