SOILS, MANURES, &c. 229 
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Gravel, or Hones, are larger maftes of 
cryftalline fubftances; they give the foil 
an open texture, and encourage the pro- 
grefs of the fibres of plants, when in 
due proportion, and not too large ; they 
are particularly beneficial to a heavy 
moift foil, permitting the water to pafs 
away more freely: on the fttrface of 
a light dry foil they tend to prevent too 
copious an exhalation, and thereby ren¬ 
der it more fertile. 
Calcareous and abforbent earths are, 
quick lime, limeftone, chalk, fhells, 
marie, &c. 
Quick lime, or cauftic calcareous 
earth, refills putrefaftion, it attrafts acids 
and oils, and deftroys both animal and 
vegetable fubftances, particularly the 
former: it is produced by burning lime¬ 
ftone, chalk, {hells, &c. with a red heat, 
till the aerial acid be difcharged; it then 
becomes 
