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the torrent has torn pieces of earth from various places, andblended them together. Nature, it would seem, having set be-fore us examples of soils fitly blended for fertility, and laid diematerials, for amending those which are not, every where tohand, has frequently left the finishing to human industry. It isin the performance of this task, that the substances of which weare now to treat come to be ranked among manures, They arethe following, viz. Virgin earth, sand, clay, burnt earth, matterleft on the soil by irrigation, refuse of salt, ashes of wood, peatand coal, soot; all of which shall be noticed in their order.
Virgin earth, by which is meant a favourable mixture of thesubstances of which the soil is composed, lying in some neglect-ed corner, and showing its aptitude to fertility by the close turfof sweet herbage which covers it. This ameliorates defectivesoils, either by itself or in composts. By itself it imparts someshare of its own happy construction, as well as the vegetablefood it has been storing up, while it remained at rest, to the soilon which it is laid. In composts it also absorbs and retains theputrid moisture oozing from putrefying substances, and servesas its vehicle to the soil.
Sand and clay , when applied on a soil of an opposite quality,must evidently correct its defects: and both have been appliedfor this purpose with considerable success. The quantity mustbe proportioned to the greatness of the defect, or otherwise itwill be of little avail.
■ Burnt earth, that is, any of the mixtures of the earths foundnear the surface, torrefied in a red heat. This operation makesa change in the modification, which produces remarkable effects.When cohesive earth has undergone this, and is afterwards re-duced to powder, all its tendency to coherence is lost, and itsparticles lie compact, without uniting. It seems to have theperfect consistence of a fertile soil: for corn springs quickly, andtillers abundantly on it: and if a little dung juice, from time totime be given, it will grow luxuriantly to maturity. It has al-so a strong tendency to promote fertility when applied on 'othersoils. When brick-dust is sprinkled on grass, a deep verduresoon after appears. When a quantity is mixed into any spot ofa corn field, a superior crop is observed for a number of years.Even a very slight torrefaction of the soil has a great effect.Mr Curtis of Lin had a succession of valuable crops by burningthe stubble on a field, f It is surprising that the beneficial ef-fects of torrefaction, which can scarcely have escaped the obser-vation of any husbandman, has not brought it more in use.Probably burnt clay might, in many cases, serve instead ofburnt lime ; and surely the one could be more cheaply procuredthan the other. If torrefied clay, upon more extensive expert-*
f Communications to tin* Board, p.- 1-30—133.