110 NO&THK)AfcOLINA GEOLOGICAL SURVEY. 



of its oxides, we are indebted for one of its most important 

 effects, the supply of the salts of ammonia, and even the or- 

 ganic salts of potash, soda, and lime. 



These facts furnish important hints relative to the proper 

 preparation of marl for the plantation, viz : that it should be 

 Composted with organic matters. We supply in this way the 

 conditions for its favorable action upon vegetation. With a 

 large quantity of organic matter, a large amount of marl may 

 be used without detriment to the vegetation, and the larger 

 the quantity the greater the amount of ammonia which will 

 be generated. For certain crops, this practice is of the high- 

 est importance. It has been proved by numerous experiments 

 with wheat, that there is a certain yield produced by the use 

 of the mineral fertilizers as phosphates of lime,- but these 

 will not increase the yield beyond a certain standard when 

 used by themselves. But if a larger supply of ammonia is 

 furnished, the number of bushels per acre is increased beyond 

 that standard. So that in order to bring lands to their full 

 capacity, ammonia must be supplied also directly, or indirect- 

 ly. A compost of marl properly made, is one of the best fer- 

 tilizers for wheat, and there is little doubt, that the favorable 

 influence is due in part, to the chemical changes which I have 

 described by which ammonia is one of the products of change. 



To estimate, therefore, the value of marl by the number of 

 pounds of phophoric acid and potash which is contained in a 

 ton, does not give its true value. All marl contains a small 

 amount of organic matter, but it is improved by adding more, 

 and thus preparing it, we provide for a continuance of those 

 changes by the instrumentality of iron until the organic mat* 

 ter is consumed, and when ammonia will cease to be genera* 

 ted. It will be understood, therefore, that organic matter is 

 necessary to effect these changes which produce the salts of 

 ammonia ; in its total absence, it is true, ammonia is produced ; 

 still, in the state of simple ammonia, it is not fit for nutrition ; 

 it requires a union with some acid, and therefore the great- 

 importance of providing all the conditions for the full action 

 of marl upon the crops to which it is applied. 



88. If the foregoing views are correct, it will be admitted 



