NORTH-CAROLINA GEOLOGICAL SURVEY. 117 



that the simple application of the oxides of iron and organic 

 matter may become the best of fertilizers. Experience has 

 proved that the scales of black oxide of iron, or the oxides and 

 other refuse matter obtained from a smith's forge are excellent 

 fertilizers for the pear and other fruit trees ; and they are no 

 doubt equally valuable for wheat and Indian corn. Iron itself 

 is always present in the ash of a plant. It is no doubt an im- 

 portant element in its organization, giving it tone and strength. 

 But as we have attempted to explain, it is equally an essen- 

 tial element in soils and marls, for its influence in effecting 

 those changes which finally result in the production of the 

 vegetable salts of ammonia, potash, soda and lime. It is in 

 this state that they are taken up by the roots of plants and 

 become thereby the effective agents of growth. 



When the functions of iron in a soil or marl are known, it 

 does not appear improbable that it is as important and as val- 

 uable as phosphoric acid or potash. In some marls it is easy 

 to recognise the change which the iron has already undergone 

 by its having become brown or reddish. This change does 

 not probably affect its qualities, though some maintain that 

 the red marl is better than the blue. The only difference be- 

 tween them is, that the protoxide of the blue has passed into 

 peroxide ; the latter may be changed back to the protoxide 

 in a soil charged with organic matter, and though I have 

 omitted to state the fact, the organic acids are capable of act- 

 ing also upon the oxide of iron and forming with them salts, 

 in which state they become fitted for reception into the cir- 

 culation of the plant. 



89. I have dwelt somewhat at length upon the importance 

 of the oxides of iron and organic matter in the soil. This 

 subject is especially interesting to planters in this State, 1st, 

 from the fact that so large a proportion of the best soils of the 

 eastern counties consist of vegetable matter in the main, and 

 2d, from another fact that the soil in the midland counties is 

 deficient in organic matter, it having been consumed by long 

 cultivation, aided, in a considerable degree, by climate. In 

 1847, I prepared an article for the American Journal of Sci- 

 ence and Agriculture, the object of which was to set forth in 



