98 NORTH-CAROLINA GEOLOGICAL SURVEY. 



Tar river. A marl, for example, which has been used as a 

 fertilizer by Hon. R. R. Bridges, contains : 



Sand or silica, 89.700 



Peroxide of iron and alumina, 5.000 



Lime, 1.500 



Magnesia, 0.200 



Potash and soda, 0.250 



Water, 3.510 



100.151 



It is evident this variety of marl cannot be transported far 

 because of its excess of sand, and in the instances in which 

 it has been employed it has been transported only a short 

 distance. These marls, however weak as they may appear, 

 frequently destroy the existing vegetation. It is due to the 

 existence of decomposing sulphuret of iron, which forms an 

 astringent salt, copperas, or a mixture of sulphate of iron and 

 alumina. This injurious salt is not formed where there is a 

 sufficient quantity of lime to neutralize the salt, in which 

 case gypsum will be formed. It should be remarked that the 

 astringent salts may exert a beneficial influence where they 

 are formed only in small quantities. 



Another similar outcrop of this sand appears in the bed of 

 a creek adjacent to the dwelling of Col. Clark, in Tawboro 7 . 

 On submitting this marl to analysis I found it composed of 



Sand, 91.300 



Peroxide of iron and alumina, 5.800 



Carbonate of lime, 0.190 



Magnesia, 0.130 



Potash, O.loO 



Soda, 0.130 



Sulphuric acid, 0.300 



Water, 1.200 



99.200 



A thin bed of the supposed upper part of the green sand 

 formation appears in the series of beds on the banks of the 

 Tar river, three miles from Tawboro . At this bank the shell 

 marl occurs in place, and has been used as a fertilizer by Col. 



