SOILS IN REFERENCE TO CLIMATE. 231 



permeable and impermeable. Acquainted with the nature of vege- 

 table earth, it is easy to judge of the advantages or disadvantages 

 which will be presented by subsoil having the faculty of retaining or 

 of permitting the escape of moisture. 



In some situations, particularly upon the slopes of hills, the layer 

 of arable land is of very limited thickness, and it is not uncommon 

 to see it lying upon rocks of the most dense description, such as 

 granite, porphyry, basalt, &c. ; in such circumstances the substrata 

 are unavailable, and there is nothing for it then in the way of ame- 

 lioration except to transport directly vegetable earth from other 

 situations. Mica schist is perhaps the least intractable rocky sub- 

 soil; the plough often penetrates it, and in the long run it becomes 

 mingled with the arable layer. It is generally agreed that limestone 

 rocks form a less unfavorable substrate. There are in fact some 

 calcareous rocks which absorb water, and crumble away, and the 

 roots of various plants, such as cinquefoin, penetrate them deeply ; 

 but there are many limestone rocks so hard that they resist all de- 

 composing action for a very long period of time. 



The qualities which we have thus far sought to determine in soils, 

 do not depend solely on their mineral constitution or their physical 

 properties, nor yet on those of the subsoils which support them. 

 These qualities to become obvious require that the soils shall be 

 placed in certain conditions which must not be left out of the reck- 

 oning. Such are those of the climate enjoyed and of the position 

 more or less inclined to the horizon in one direction or another. 

 The precepts which we have laid down are especially applicable to 

 the arable lands of Germany, England, and France. But in gener- 

 alizing it would be proper to say that clayey lands answer better in 

 dry climates, and light sandy soils in countries where rains are fre- 

 quent. Kirwan made this remark long ago in connection with nu- 

 merous analyses of wheat lands. The conclusion to which this 

 celebrated chemist came was this, that the soil best adapted for wheat 

 in a rainy country must be viewed in a very different way with refer- 

 ence to a country where the rains are less frequent. The fertility 

 of light sandy soils is notoriously in intimate relationship with the 

 frequent fall of rain. At Turin, for example, where a great deal of 

 rain falls, a soil which contains from 77 to 80 per cent, of sand is 

 still held fertile, while in the neighborhood of Paris, where it rains 

 less frequently than at Turin, no good sod contains more than 50 pei 

 cent, of sand. A light sandy soil which in the south of France 

 would only be of very inferior value, presents real advantages in the 

 moist climate of England.* Irrigation supplies the place of rain, 

 and in those countries or situations where recourse can be had to it, 

 the question in regard to the constitution of soils loses nearly the 

 whole of its interest. Land that can be irrigated has only to be 

 loose and permeable in order to have the whole of the fertility de- 

 veloped which climate and manure can confer. Sandy deserts are 

 sterile because it never rains. Upon the sandy downs of the coasts 



* Sinclair's Practicul Agriculture. 



