40 CHYMISTRY APPLIED TO AGRICULTURE. 



cultivated upon it. The bed of earth ought to be from 10 to 

 12 inches in depth for grain, and much more than that for 

 clover and sainfoin; for trees it must be much deeper 

 than for these, otherwise their roots, running but little be- 

 low the surface of the ground, will extend their shoots to 

 a great distance, and thus exhaust the strength of a large 

 • portion of soil. Trees are often found upon the sides of 

 mountains, which are almost entirely devoid of a covering 

 of earth, but in this case the chinks and crevices of the 

 rocks supply the place of earth, or rather the rocks are of 

 so spongy and porous a nature, as to permit the roots to 

 penetrate them. In the Cevennes and Limousin the 

 most beautiful chestnuts are planted upon granite and 

 ■free-stone; and the famous vines of the Hermitage pros- 

 per in a soil of granite decomposed at the surface. 



It is not immaterial of what substance the sub-stratum 

 of the beds of earth are composed ; if it be of sand, the 

 soil above will dry more quickly than if it were of marl or 

 clay. A bed of clay under one of sand contributes to its 

 fertility by retaining the water, which easily filters 

 through the last, and thus preserving its humidity ; but if 

 the water collected upon the clay moisten for too long a 

 time the roots of the plants, they become languishing. I 

 have always observed that roots might be exposed to living 

 and flowing water, without being injured by it, but that 

 stagnant water is always hurtful, and, for the most part, 

 destructive to them. Agriculturists have learned this by 

 •experience, and hence has arisen the custom of draining 

 their fields and meadows. In lands which are too moist, 

 a good effect is produced by forming beds of flints, or peb- 

 bles, upon which a layer of mould may be placed ; I have 

 seen excellent meadows made in this way, upon land which 

 had never before produced any thing but rushes. 



A clayey or marly soil, which lies upon a bed of calca- 

 reous and porous rock, is more fertile than one which rests 

 upon a foundation of hard rock, impermeable to water ; 

 the reason of this is very simple ; in the first case, the wa- 

 ter filters through the rock, and escapes ; in the second it 

 remains stagnant, rendering pasty a soil possessing none 

 of the requisites for vegetation. 



The situation of land causes a great variety in its fertili- 

 ty, and in the nature of its productions ; lands which have a 

 southern exposure dry more quickly than those lying towards 



