124: NORTH-CAUOLINA GEOLOGICAL SURVEY. 



promoted, and the revenue upon the railroads increased ; and 

 in the end, it might, and invariably would supplant guano, 

 which is a drain upon the pockets of planters. 



91. In order to free the sand from adherent marl, it might 

 be passed through a cylinder, the inside of which had many 

 projecting angles, and within which another cylinder studded 

 with angular rods should be made to revolve rapidly, while 

 the marl and water was passing through them. The sand, 

 after issuing from the machine, would subside almost imme- 

 diately, while the lighter marl would pass forward and be 

 allowed to subside in vats. With a machine properly con- 

 structed, a hundred tons of marl might be washed in a day, 

 and though all the sand might not be removed from it, yet a 

 very large proportion would be. Some of the marls, as 

 analysis proves, contain seventy-five per cent of sand. The 

 concentration consequent upon its removal would convert it 

 into a fertilizer which would contain three or four times its 

 amount if it was in its natural state. The washed marl would 

 then possess the following composition : 



Phosphate of lime, 2.50 



Peroxide of iron and alumina, 25.00 



Carbonate of lime, 44.17 



Magnesia, 1.71 



Potash, 2.35 



Soda, 2.50 



Sulphuric acid 0.72 



Chlorine, 0.52 



Organic matter, 1 6.12 



Soluble silica, 0.78 



Water, 3.75 



The commercial value of marl of this description will be 

 from 8 to 9 cents per bushel. A bushel of dry rnarl weigh- 

 ing eighty pounds, and twenty-five bushels weighing two 

 thousand pounds, it will be worth from $1 60 to $1 80 per 

 ton. Fifty tons of marl might be washed per day, which 

 would give about twelve tons of concentrated marl in the 

 vats. The cost of raising and washing may be performed at 

 from 37-J to 50 cents per ton, and perhaps less than the low- 

 est figure. 



