SOILS. The agricultural soils which have been formed fa In the disintegration and de composition of the primitive rocks, such as granite, basalt, E. late or limestone, and especially those which contain all these minerals minutely divided and intimately mixed, are always naturally fertile, and soon enriched by cultivation ; the hard particles of quartz main tain a certain porosity in the soil, which allows air and moisture to circulate, while the alumina prevents its too rapid evaporation or filtration. The soils which have been evidently formed from the rocks which arc supposed to be of secondary formation, are fertile accor ding to the proportion of the earths of these rocks which they contain.
Each distinct formation gives rise to a great variety with respect to fertility, even where the basis remains the same ; but it is of great importance to the farmer to ascertain the general nature of the rocks and strata on which his farm is incumbent, and no chemical analysis can determine the exact value of the land unless the geological situation of it is distinctly known.
The alluvial soils formed by the deposit of a variety of earths in a state of great division, and mixed with a considerable portion of organic matter, form by far the most productive lands. They will bear crop after crop with little or no additional manure, and with a very slight cultivation. These soils are found along the course of rivers which traverse extensive plains, and which have such a current as to keep very fine earth suspended by a gentle but constant agitation, but not sufficiently rapid to carry along with it coarse gravel or sand.
The simplest process of ascertaining the mechanical texture of soils is by washing with pure water. For this purpose nothing is required but a few flat plates and large cups.
Some of the soil is formed into a very thin mud by stirring it in a cup nearly full of water. The finer particles are successively poured off fiom the sand or grit, which at last remains pure, so that the water added to it is no longer discoloured. This being dried and weighed, gives the coarse sand. The water and earth poured off are allowed to settle. A common soup-plate is found a very convenient vessel for this purpose. On the surface of the deposited earth will be found all the undo composed vegetable matter, which with a little care is easily taken off, dried, and weighed. The finer portions of the earth can be poured off successively by shaking the whole mode rately, till nothing but very fine sand remains. The alumina and impalpable silica will re main long suspended in the water, and allow any sand yet remaining to he deposited. They may be rapidly separated from water by filtration through stout blotting-paper ; but it is preferable to pour them into a glass tube about one inch in internal diameter, with a cork fitted in the lower end. In this tube the earths slowly fall to the bottom, and any variety in the size of the particles causes aline more or less distinct, which can be observed through the glass ; and thus a very good idea may be obtained of the proportion of the dif ferent earths, as far as regards the size of their particles. In order to ascertain their chemical differences, they should be taken to a chemist and analysed.
The chemical and mechanical modes of treating various kinds of soil are briefly noticed under the names of the soils [Cumac ; CLAY; LOAM; MARL; ; also under 111rtruan, &c.