MINERAL CONSTITUENTS OF SOIL. 209 



respect, then, our soils are peculiar, and hence the great im- 

 portance attached to this substance as a manure. (See im- 

 provement of the soil.) The reason why so small a quantity 

 of carbonate of lime is found in our soils, compared with those 

 in other countries, is ascribed by Prof. Hitchcock to the fact 

 that growing plants abstract it, and that our lime rocks are 

 not so easily reduced to the state of soil by the ordinary 

 agents of disintegration. 



The influence of lime upon growing vegetables is not, in 

 this country, due to the texture which it gives to the soil, for 

 in most cases, the quantity is not sufl[icient to render a heavy 

 soil light, or modify the influence of too great a quantity of 

 siliceous sand. Its influence is probably threefold. 1. It 

 tends to convert the vegetable matter into vegetable food, 

 thus performing the office of a solvent, or converter of innu- 

 tritious matter into nutriment. 2. It corrects the acidity of 

 soils, by uniting with free acids, or decomposing poisonous, 

 metallic salts. 3. It forms a part of the vegetable struc- 

 ture, and is properly inorganic food. Like all other alkalies 

 it also contributes to electrical effects, which may be regarded 

 as a kind of stimulus to the vital functions. It is found, as 

 we have seen, in the vegetable productions, sometimes uni- 

 ted with organic, and at others, with inorganic acids. 



4. Magnesia. Magnesia is found in serpentine in the 

 form of a silicate, in steatite or soap-stone, talcose slate, in 

 magnesite, sea water, certain limestones, called magnesian 

 limestone or dolomite. Although generally found in soils, it 

 never constitutes but a small portion of them. The quan- 

 tity is given in but a hw of the soils of Massachusetts, and 

 varies from .25 to 2J per cent, from which it is inferred, that 

 only traces of it exist. In the soils of Rhode Island, the 

 amount of magnesia is rarely 1 per cent. ; often none at all, 

 or only traces are found. A few soils contain 4 per cent. 

 In New Hampshire less than 1 per cent, is found, and in 

 Maine, out of thirty-five soils analyzed, only one contained 

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