9 
NATURE AND OFFICES OF EARTHS AND SOILS, 
1. Earths and Soils being the laboratory wherein the food or nutriment of 
the plant is prepared, and the media through which it is conveyed to the roots ; it 
becomes a matter of primary importance to the gardener and agriculturist, to obtain 
correct ideas of their component parts, and of the offices they perform in the work 
of vegetation. It will also be very useful to acquire a method of general classifica- 
tion, so as to arrive at some degree of precision and systematic arrangement ; on 
this subject, says the Encyclopaedia of Gardening, at No. 1031. 1. u A correct 
classification of soils may be founded on the presence or absence of organic or inor- 
ganic matter in their basis. This will form two grand classes, viz., pruivitive soils, 
or those composed entirely of inorganic matter ; and secondary soils, or those com- 
posed of organic and inorganic matter in mixtures. These classes may be subdivided 
into orders, founded on the presence or absence of saline, metallic, and carbonic 
matter. The orders may be subdivided into genera, founded on the prevailing 
earths, salts, metals or carbon ;the genera into species, founded on their different 
mixtures ; the species into varieties, founded on colour and texture ; and sub- 
varieties, founded on moisture, dryness, richness, lightness, &c." 
In naming the genera, the first thing is to discover the prevailing earth or earths ; — - 
" thus," Sir Humphry Davy has observed, " the term sandy soil should never be ap- 
plied to any soil that does not contain, at least, seven-eighths of sand ; sandy soils 
that effervesce with acids should be distinguished by the name of calcaneus, (chalky) 
sandy soils, to distinguish them from those that are silicious," (of the nature of 
flint.) " The term clayey soil should not be applied to any land which contains 
less than one-sixth of impalpable earthy matter, not considerably effervescing with 
acids." The word loam should be limited to soils containing at least one-third of 
impalpable earthy matter, copiously effervescing with acids. " In general, the 
soils, the materials of which are the most various, are those called alluvial, or 
which have been formed from the depositions of rivers ; and these deposits may be 
designated as silicious, calcarious, or argillaceous (clayey) ; and, in some oases, 
the term saline may be added as a specific distinction, applicable, for example, at 
the mouths of rivers, where their alluvial remains are overflowed by the sea." 
2. The qualities and value of soils are discoverable botanically, and by che- 
mical analysis. First, botanically, that is, by the plants which grow on them na- 
turally. " The saintfoin (heydesarum onobryitris) is almost always an indication 
of a calcarious soil ; the common colt's-foot, (tussilago-farfara,) of blue clay ; pur- 
ple sandwort, (arenaria rubra,) of poor sand ; the common wood sorrel (oralis 
acetosella,) of the presence of iron." Secondly, by chemical analysis. The quan- 
tity of soil best adapted to a perfect analysis is stated to be four hundred grains ; it 
should be collected in dry weather, and exposed to the air till it become dry to the 
touch. The process of analysis is complicated, and one of extreme nicety. Some 
cultivators may be qualified to perform the necessary operations, but in general a 
VOL. IV.— no. xxxvn. c 
