336 Observations on Manures , &c. 
t 
respect, and much is doing by the British government in the 
West Indies. 
Agriculturists have many vague denominations of soil, such as 
clay, loamy, marly, sandy, limestone, limestone gravel, sandy 
gravel, stoney, poor light soil, rich black soil. These aretole- 
rably descriptive in a general way ; but as the theory of the art 
improves, we shall need more accuracy. Of the primitive earths, 
none need be noticed under this section, but silex or sand ; argil 
or clay: and calx or lime. The others have never been yet found 
in sufficient quantity to produce any notable effect, except in the 
hurtful quality of magnesia when combined with lime, as 2 to 3 
first noticed by Mr. Tennant. It is evident that for the mechanical 
purpose of increasing or lessening adhesion, supporting the plant, 
and admitting its fibres to shoot more freely, clay, sand, and lime- 
stone are mutually manures to each other ; acting mechanically 
by their mixture. Thus in Cheshire and Norfolk, in England, 
the clay and marl pits furnish an excellent and permanent manure 
to the sandy soil above ; and assist moreover in retaining manure 
and imbibing moisture. 
But it is not merely the mechanical mixture of soils that may 
be useful; for the experiments of M. D’abrcet and M. Faroni 
have shewn us, that in the temperature of 100° of Fahr. different 
earths have different capacities for retaining moisture ; so that by 
judicious admixtures, this valuable property in soils may be in- 
creased or diminished ; and as none of the earths are found per- 
fectly pure in soils, (clay, for instance, retaining 66 per cent, of 
sand without losing its distinctive character) tive character) a 
field is opened for ascertaining this property in different admix- 
tures and combinations. For Mr. Wedgwood discovered that 
earths would chemically combine in the moist way. 
Besides the tenacity of soils, and their capability of retaining 
moisture, their dcfith is also to be considered by the cultivator. 
Some plants have long tap-roots, such as rhubarb, liquorice, car- 
rots, parsnips, madder, Sec. These are evidently unfit for any 
soils, but of loose adhesion and of considerable depth. Equally 
preposterous would it be to use a soil like the Genesee fiats, of 20 
feet deep of light, rich mould, for grasses that spread upon the 
surface. Again, where soils are naturally sandy, dry, and arid and 
the climate warm, plants should be selected, whose roots penetrate 
deep and beyond the influence of atmostpheric evaporation. Thus, 
in this country as in the south of France, Lucerne, ( medicci ) and 
