206 SOIL SAND AND CLAY. 



chemical composition of soils Chemists of great talent have made 

 mafny complete analyses of soil ; noted for their fertility ; still practical 

 agriculture has hitherto deriv^id very slender benefits from labors of 

 this kind. The reason of this is very simple ; the qualities which we 

 esteem in a workable soil depend almost exclusively upon the me- 

 chanical mixture of its elements ; we are much less interested in its 

 chemical composition than in this; so that simple washing, which 

 shows the relations between the sand and the clay, tells, of itself, much 

 more that is important to us than an elaborate chemical analysis. 

 The quality of an arable soil depends essentially on the association 

 of these two matters. Sand, whether it be silicious, calcareous, or 

 felspathic, always renders a soil friable, permeable, loose ; it facili- 

 tates the access of the air and the drainage of the water, and its in- 

 fluence is more or less favorable as it exists in the state of minute 

 subdivision, or in the state of coarse sand or of gravel. 



Clay possesses physical properties entirely opposed to those of 

 sand ; united with water it forms an adhesive plastic paste, which, 

 once moistened, becomes almost impermeable. With such charac- 

 ters, it will easily be conceived how it is impossible to work to ad- 

 vantage a soil that is entirely argillaceous. The proper character, 

 or, if you will, the quality of a soil, depends, then, essentially on 

 the element which predominates in the mixture of sand and clay that 

 composes it ; and between the two extremes, which are alike un- 

 favorable to vegetation, viz., the completely sandy soil and the un- 

 mixed clay, all the other varieties, all the intermediate shades can 

 be placed. It is rare, indeed, that arable soils are formed solely of 

 sand and clay : not to mention certain saline substances which are 

 generally encountered, although in small quantity, we always find 

 the remains of organic matters, remains which constitute that part 

 of a soil which has been designated under the somewhat vague name 

 of humus. Although a soil which is entirely without humus may be 

 cultivated by calling in the aid of manure, and as humus, consequent- 

 ly, need not be regarded as indispensable, still this matter generally 

 enters, in certain proportions, into the constitution of soils. The 

 soils of forest lands contain a large quantity of it, and some soils are 

 mentioned which are very rich in this substance, and which yield 

 abundant irops of grain for ages, and with very little attention. 



In examining a soil, attention ought to be directed, 1st, to the 

 sand, 2d, to the clay, 3d, to the humus which it contains. It would, 

 further, be useful to inquire particularly in regard to certain other 

 principles which exert an unquestionable influence upon vegetation, 

 such as certain alkaline and earthy salts. 



Vegetable earth dried in the air until it becomes quite friable 

 may, nevertheless, still retain a considerable quantity of water, and 

 which can only be dissipated by the assistance of a somewhat high 

 temperature. It is therefore proper, in the first instance, to bring 

 all the soils which it is proposed to examine comparatively, to one 

 constant degree of dryness. The best and quickest way ff drying 

 such a substance as a portion of soil, is to make use of the oil-bath ; 

 a qiantity of oil contained in a copper vessel is readily kept at ai 



