NOKTH-CAROLINA GEOLOGICAL SURVEY. 91 



or consolidated parts of it are abundant on the plantation of 

 Maj. Collier. 



At a few places it is sufficiently pure to be burnt for lime ; 

 as a general rule it contains too much silex to make a strong 

 lime. 



The rock on Maj. Collier's plantation contains : 



Silica, 59.400 



Peroxide of iron in combination with ) 4 120 



alumina and phosphoric acid, i ' ' 

 Carbonate of lime and a trace of magnesia, 36.480 



100.000 



The amount of carbonate of lime is variable, and ranges 

 in the consolidated varieties from 30 to 75 per cent. The 

 silex in the rock exists in grains as sand, which are visible, 

 but a soluble silica is no doubt the cementing material, which 

 of course once existed in solution, or in a state of minute 

 subdivision. This marl may be used in building, or if suffici- 

 ently pure and free from sand and silica, it may be burnt for 

 lime, which will be adapted to agricultural purposes. Its 

 composition fits it for this purpose as it contains a small pro- 

 portion of phosphoric acid. 



63. The green sand is frequently partially consolidated, 

 but never forms a building material. For agriculture, when 

 the amount of potash is considered, it is the most important 

 of the marls. In North-Carolina I have found no locality 

 where its potash equals that of New Jersey. This I attribute 

 in part to our inability to reach strata which are upon the 

 same geological level, though it is probable that the amount 

 of sand will be greater, and hence diminish proportionally 

 the amount of available fertilizing matter. 



The lowest mass accessible at Blackrock I found by analy- 

 sis, has the following composition : 



Silex and sand, 37.000 



Peroxide of iron and alumina, 6.400 



Carbonate of lime, 33.400 



Phosphates of peroxide of iron, 1.600 



Soluble silica, 1.460 



