32 Soil. 



stubble, and roots of grain crops, on arable ( IOS ). It is an es- 

 sential ingredient in all fertile soils, and is of great use, by 

 attracting and retaining a due proportion of moisture, in 

 the mixed mass which the soil contains. Its formation on 

 grass lands is extremely slow ; for it is calculated,- that it 

 proceeds at the rate of only one inch in a century ( I09 ). Con- 

 siderable accumulations of mould however, may be produced 

 from the leaves of trees, amassed for a number of years, 

 and rotted on the surface ( II0 .) When, in addition to vege- 

 table, there are animal substances in a state of decomposi- 

 tion, the soil is distinguished for its fertility. 



3. It is of essential consequence, when the surface is bare, 

 and exposed to the rays of the sun, that the colour of the 

 soil should be such, as to attract and absorb the greatest 

 heat from the sun and the atmosphere, more especially in 

 spring. 



Soils are of various colours. The principal are white, 

 black, and red. Uniformity of colour, is always a more fa- 

 vourable indication of fertility, than when they are mottled, 

 which is generally owing to an inferior subsoil. The soil 

 of the Carse of Gowrie, in Scotland, so celebrated for its 

 fertility, is of a pale colour, from a white clay which forms 

 its subsoil. 



White stiff clays are heated with difficulty, and being 

 usually very moist, retain their heat only for a short time. 



A black soil, containing much vegetable matter, is most 

 easily heated by the sun and air. Its temperature has in- 

 creased from 65 to 88 by exposure to sunshine for an 

 hour. A chalky soil, under the same circumstances, was 

 heated only to 69. In the shade, however, the black mould 

 lost its heat more rapidly ( 1IX ). 



The red colour in some soils proceeds from a combina- 

 tion of iron ; but it does not appear that a reddish colour 

 is defective in fertility ; on the contrary, much land, where 

 the soil, subsoil and minerals are nearly of the colour of 

 brick, is fertile, and produces excellent crops. Red soils 

 are greatly improved by calcareous manures, as the chalky 

 are by ashes containing a considerable proportion of iron. 



4. It has been justly remarked, that too much can hardly 

 be paid for a good soil, and that even a low rent will not 

 make a poor one profitable. The labour of cultivating a 

 rich and a poor soil is nearly the same; while the latter 

 requires more manure, and consequently is more expensive. 

 Poor soils, at the same time, may have such a command 

 of lasting manures, as lime or marie, or even of temporary 



