SOILS. 15 



11 But the above classification has reference only to the clay and sand, while we know 

 that lime is an important constituent of soils, of which they are seldom destitute. We have 

 therefore, 



&quot; 7th. Marly soils, in which the proportion of lime is more than 5 per cent., but does 

 not exceed 20 per cent, of the whole weight of the dry soil. The marl is a sandy, loamy, or 

 clay marl, according as the proportion of clay it contains would place it under the one or the 

 other denomination, supposing it to be entirely free from lime, or not to contain more than 

 5 per cent., and 



&quot;8th. Calcareous soils, in which the lime, exceeding 20 per cent., becomes the distin 

 guishing constituent. These are also calcareous clays, calcareous loams, or calcareous sand, 

 according to the proportion of clay and sand which are present in them. The determination 

 of the lime, also, when it exceeds 5 per cent., is attended with no difficulty. 



&quot;To 100 grs. of the dry soil diffused through half a pint of cold water, add half a wine 

 glass full of muriatic acid (the spirit of salt of the shops), stir it occasionally during the 

 day, and let it stand over night to settle. Pour off the clear liquor in the morning, and fill 

 up the vessel with water to wash away the excess of acid. When the water is again clear, 

 pour it off, dry the soil and weigh it; the loss will amount generally to about one per cent, 

 more than the quantity of lime present. The result will be sufficiently near, however, for 

 the purposes of classification. If the loss exceed 5 grs. from 100 of the dry soil, it may be 

 classed among the marls; if more than 20 grs , among the calcareous soils. 



; Lastly, vegetable matter is sometimes the characteristic of a soil, which gives rise to a 

 further division of, 



&quot; 9th. Vegetable molds, which are of various kinds, from the garden mold, which contains 

 from 5 to 1 per cent., to the peaty soil, in which the organic matter may amount to 60 or 

 70 per cent. These soils also are clayey, loamy, or sandy, according to the predominant 

 character of the earthy mixtures. 



&quot; The method of determining the amount of vegetable matter for the purposes of classi 

 fication, is to dry the soil well in an oven, and weigh it; then to heat it to dull redness over 

 a lamp or bright fire till the combustible matter is burned away. The loss on again weighing 

 is the quantity of organic matter.&quot; 



The preceding are commonly recognized as such general divisions as possess properties 

 sufficiently common to require a similar process in testing. The earthy, or what are termed 

 inorganic parts of soils, are found almost exclusively in combination with earths, salts, or 

 minerals, and constitute from less than one-half of one per cent, to over 10 per cent, of all 

 plants; in addition to these inorganic parts, fertile soils must also contain carbon, oxygen, 

 nitrogen, and hydrogen, which are called organic parts of soils, because of their greater pro 

 portion in vegetables and animals, of which they constitute in substance from about 90 to 

 over 99 per cent. 



Clay Soils and their Management. From their affinity for water, and a ten 

 dency to hold it in such quantity as to often impede a rapid or luxuriant growth of vegetation, 

 clay soils are commonly denominated cold and wet. 



Clay owes its origin mainly to the decomposition of other minerals, and consists largely 

 of alumina, which is the most abundant of all the earths, combined with silica and water, 

 its plasticity being due to the alumina it contains, which being so fine in texture and com 

 pact, prevents the escape of water resting upon the surface of such soils, or contained within 

 it. In its pure state, alumina is an earth resembling soft, white powder, without taste; in its 

 crystaline form, it occurs as sapphire and ruby, which are among the hardest and most val 

 uable of the precious stones. 



Prof. Brewer states that when on bottom lands, or in valleys, clays are usually the sedi 

 ment deposited from muddy water in some earlier age of the earth s history, but when on 

 hillsides, they are often, in part at least, due to the decay of slate rocks. 



