MARLY AND CALCAREOUS SOILS, AND VEGETABLE MOULDS. 233 



soil contain 60 of sand, or 40 in 100 (40 per cent.) It would, therefore, 

 be properly called a loam, or loamy soil. ^ 



But the above classification has reference only to the clay and sano; 

 while we know that lime is an important constituent of soils, of which 

 they are seldom entirely destitute. We have, therefore, 



7°. Marly soils, in which the proportion of lime is more than 5 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 other denomination, sup- 

 posing it to be entirely free from lime, or not to contain more than 5 per 

 cent., and 



8°. Calcareous soils, in which the lime exceeding 20 per cent, becomes 

 the distinguishing constituent. These are also calcareous clays, calca- 

 reous loams, or calcareous sands, 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. 



To 100 grs. of the dry soil diffused through half a pint of cold water, 

 and half a wine-glass full of muriatic acid (the spiritof saltof the shops), 

 stir it occasionally during the day, and let it stand tver-nlght to settle. 

 Pour ofTthe 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 



9°. Vegetable moulds, which are of various kinds, from the garden 

 mould, which contains from 5 to 10 per cent., to the peaty soil, in which 

 the organic matter may amount to 60 or 70. These soils also are clayey, 

 loamy, or sandy, according to the predominant character of the earthy 

 admixtures. 



The method of determining the. amount of vegetable matter for the 

 purposes of classification, is to dry the soil well in an oven, and weigh 

 it; then to heat it to dull redness over a lamp or a bright fire till the 

 combustible matter is burned away. The loss on again weighing is the 

 quantity of organic matter. 



Summary. — The several steps, therefore, to be taken in examining a 

 soil with the view of so far determining its constitution as to be able pre- 

 cisely to name and classify it, will be best taken in the following order : — 



1°. Weigh 100 grains of the soil, spread them in a thin layer upon 

 white paper, and place them for some hours in an oven or other hot 

 place, the heat of which may be raised till it only does not discolour the 

 paper. The loss is water. 



2'\ Let it now (after drying and weighing) be burned over the fire as 

 above described. The second loss is organic, chiefly vegetable matter, 

 with a little water, which still remained in the soil after drying. 



3°. After being thus bu7:>3d, let it be put into half a pint of water 



