SOILS, MANURES, &c. 231 
— -T ■ - -- ■ — -- , - , -- - - - -T- - -■ 
friable in water, and effervefces with 
acids, which diftinguifh.es it from Ample 
# 
clay. 
Vegetable fubftances are found on and 
near the furface of moft foils; they confift 
of the roots and fibres of plants, and of 
plants that have grown, fallen, and de¬ 
cayed there; they contain only particles, 
which give the foil a black or dark 
coloured appearance, and greatly enrich 
it, unlefs the plants happened to be of 
the acetofe, aftringent, and antiputre- 
fcent kind. 
Vegetable fubftances pafs through the 
faccharine, vinous, and acetous fermenta¬ 
tions, before putrefaction is completed, 
and their conftituent parts feparated. 
Metallic, or mineral fubftances, are 
frequently found in foils united with an 
acid ; they are extremely pernicious and 
1 
poifonous to plants, and, where they 
abound 
