23 CHYMISTRY APPLIED TO AGRICULTURE. 



Water, by its own action, will penetrate by degrees into 

 the earthy principles of rocks, and produce, at length, the 

 effect mentioned above ; but its power is wonderfully in- 

 creased, whilst passing from its liquid state, to that of ice. 



As soon as the surface of a rock is furrowed, and the 

 mosses and lichens have fastened themselves upon it, all 

 the plants which require but little nourishment, take root 

 and decay there in turn ; and the product of each succes- 

 sive decomposition adds something to the slight bed of 

 earth formed by the first, till in time a soil is produced, 

 fit for cultivation. 



Hitherto we have considered only those circumstances 

 which explain to us the formation of arable lands ; these 

 causes have, without doubt, placed at our disposal all the 

 lands which are appropriated to agriculture ; but the hand 

 of man and the successive generations of plants have 

 rendered them still better suited to this purpose. 



The great stones which injured the harvests upon allu- 

 vial soils, have been removed by blasting. The soils 

 which were too stiff have been improved by a suitable 

 admixture of other earths ; all the soils have been in turn 

 manured by the remains of plants, or the collections of 

 the barn-yard ; and man has learned by experience what 

 kind of culture, and what species of plants are suited to 

 each soil. Nature has prepared the materials, man dispo- 

 ses of them in such a manner as to cause them to produce 

 according to his necessities, or his tastes. 



But in what does the difference of soils consist ? and 

 which are those best suited to agriculture 1 



In examining the nature and variety of the rocks, of 

 which all arable lands were originally but the ruins ; and 

 which, notwithstanding all the labor of man, preserve their 

 primitive characters, we shall find the following varieties. 



Amongst rocks of the first formation, or, as they are call- 

 ed, primitive rocks, granite holds the first rank ; it is gene- 

 rally formed by the aggregation, more or less compact, of 

 several stones, differing among themselves in form, color, 

 hardness, and composition ; these stones are, most com- 

 monly, feldspar, quartz, and mica. These elements of 

 granite, also, separately form rocks, in which only two 

 of them are combined, as in micaceous schist, which is 

 composed of quartz and mica, disposed in beds, sometimes 

 curvilinear ; quartz forms by itself, nearly without mix- 

 ture, some of the primitive mountains. 



