92 
ECONOMICAL MINERALOGY. 
stalline structure, and disintegrate into grains which often have the appearance of coarse sand, 
and which indeed in some cases are more or less mixed with siliceous particles. Such are 
the dolomitic limestones of the counties of Westchester, Putnam, Dutchess, Jefferson, Frank¬ 
lin and St. Lawrence. Not unfrequently patches of this sandy or granular limestone are en¬ 
tirely destitute of vegetation; a circumstance which is, I think, to be chiefly ascribed to the 
mechanical constitution of the materials which compose them. 
Another important conclusion to be drawn from the facts stated in regard to the western 
soils is, that magnesia in the mild or carbonate state, when mixed with carbonate of lime, 
exerts a beneficial rather than a deleterious influence. It was long since stated by Mr. Ten¬ 
nant, that a lime which contained magnesia was injurious to vegetation; and he also ascer¬ 
tained by experiment, that seeds sown upon a soil mixed with some calcined magnesia, either 
died or vegetated in a very imperfect manner, and that the plants were never healthy. Hence 
a prejudice soon arose against all magnesian limestones ; and it was thought by many agri¬ 
culturalists that this earth, in whatever form it was applied to the soil, must prove injurious 
to it. 
Davy, in his Agricultural Chemistry, has placed this subject in its true light; for while he 
admits the correctness of Mr. Tennant’s opinions, he at the same time gives reasons which 
induce him to believe that magnesian limestone, or carbonate of magnesia, is a fertilizing 
agent. Thus he observes that one of the most fertile districts in Cornwall, the Lizard, is one 
in which the soil contains carbonate of magnesia. The correctness of this observation has 
been confirmed by Prof. Giobert, who has announced that this earth is abundant in the most 
fruitful soils in the vicinity of Castelmonte, and that there are numerous localities of a similar 
kind in Piedmont. So also M. De Gasparin, in his memoir on soils, states that the carbonate 
of magnesia is contained in great quantities in the soils of the valley of the Nile ; while, ac¬ 
cording to the same author, those of Bas Languedoc often furnish from eight to thirty-three 
per cent.* 
Now carbonate of magnesia is a constituent of many of the western rocks, and must have 
entered largely into the composition of the soils which cover them. It exists in the proportion 
of twenty-five to thirty per cent, in the limestones of Rochester, Monroe county, and in those 
of Lockport in the county of Niagara. It is also found in the caiciferous slate of Chittenango, 
and in all the water limestones which I have examined,! whether from Madison, Onondaga or 
Erie counties. Now the soils in the immediate vicinity of these magnesian rocks, so far from 
being sterile, are among the most fertile in the State. 
If the above facts are to be relied on, we shall probably have the means of arriving at some 
certain results in regard to the action of magnesia upon soils, whether it be applied to them 
in the natural state as a carbonate, or in that state of causticity to which this is brought by 
the ordinary process of lime-burning. 
The following are suggested as being thus deducible : 
* Edinburgh Nnv Philosophical Journal, XXVII. 84. 
f See the Tables showing the composition of several of our common and hydraulic limestones, pages 74 and 82. 
