NOKTH-CAKOLINA GEOLOGICAL SURVEY. 99 



Clark with good success for many years ; the relative position 

 of this upper bed of green sand is represented in a section 

 already described. It lies, as will be seen, immediately be- 

 neath the shell marl ; and beneath the green sand a gray 

 sand crops out, which is quite consolidated, and to the eye 

 appears much like a limestone formation, but, as will appear 

 in the sequel, is a bed of sand of unknown thickness. 



The upper mass of green sand, which does not exceed four 

 feet, has a similar composition to those already noticed. It 

 is composed of 



Sand 79.000 



Peroxide of iron and alumina, 8.800 



Carbonate of lime, 2.752 



Magnesia, 1.600 



Potash, 1.739 



Soda, 0.300 



Soluble silica, 0.600 



Sulphuric acid 0.200 



Organic matter, 2.000 



Water, 2.330 



99.321 



69. Although the proportion of sand is large in this marl, 

 yet I believe it is a more valuable fertilizer than the shell 

 marl above it. 



It contains more potash than the green sand of Black rock 

 on the Cape Fear. It contains, it is true, less lime, but if the 

 composition of the ash of the cotton stalk is consulted it will 

 be perceived that magnesia is also required this marl con- 

 tains a large percentage of this substance. 



It may be regarded as containing seventeen or eighteen 

 per cent, of fertilizing matter. ~No trial has been made of 

 this stratum, and of course nothing can be said upon the 

 ground of trial. 



70. A very useless bed of gray sand occupies the bank 

 at the water's edge, which has been alluded to. Neverthe- 

 less, I submitted a specimen of it to analysis. It is one of 

 those beds which is charged with sulphuret of iron, and forms 

 astringent salts, on decomposition, of the sulphuret of iron 



