SCIENTIFIC AGRICULTURE. 155 



It is apparent now, that the soil bears no necessary resem- 

 blance in all cases to the rocks on which it lies, except when 

 derived directly from them ; then it partakes of their nature. 



After the surface of rocks has by these agencies become 

 sufficiently pulverized and decomposed to form a thin layer of 

 soil, lichens and mosses succeed in fixing their roots in it, 

 causing at the same time further disintegration of the rocks, , 

 and increase of the soil" by their annual decay. When the- 

 soil becomes in this way of sufficient depth and fertility to 

 nourish other, larger, and more perfect species of plants, vegetai- 

 tion becomes more abundant: the decay of this, together with; 

 the organic and earthy matters of animals, which are returned 

 to the soil, combined with the art. and industry of man, a 

 soil sufficiently deep and fertile for successful cultivation, is in 

 process of time produced. 



A general knowledge of the rocks, metals and earths, is of 

 great value to the agriculturist, in enabling him, by the indi-- 

 cations which they afford, to discover springs, mineral waters, 

 ores, mines of coal or metal, marl, lime, valuable stones, &c. ; 

 and also to direct him. to the best locations for lime kilns, glass- 

 houses, brick kilns, potteries, foundries,; salt works, bath houses 

 and stone quarries. Modern chemistry has shown that almost 

 every substance is a compound of several others, and future- 

 experiment may yet show us the compound nature of many 

 bodies which are now considered elementary. There would be 

 little difficulty in determining the character of any soil, had we 

 only to consider the constitution of the rock from which it was 

 originally derived. 



But, during the lapse of ages, the various causes which have 

 been in operation have so changed them that their primitive 

 character has almost disappeared, and they must be considered 

 in thehvpresent actual conditions. Arable soils consist mainly 

 of silex and alumina, with some lime, iron,, sodium, potassium. 



