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For these reasons, it is always expedient to dig the chalk in the beginning of winter, and to spread it immediately upon the field as well as can be done, so as to expose it to the vicissitudes of the winter weather before it has had time to harden after being taken from the pit.
As the chalk ought always to be carried to the field while yet wet, it in a great measure prevents those who may be at a distance from the place where it is found, from being benefited by this manure; because the carriage of it would, in these circumstances, be extremely burdensome.
To obviate this inconvenience, it becomes a very oeconomical practice to reduce it to the state of lime before it is carried home. For, in this way, the weight is not only much diminished by the dissipation of all L 11 the the moisture from the chalk, but it can also be carried home in summer, when the weather and roads are the best; and a much smaller quantity will produce an equal effect, than, when it is in the state of chalk.
Those, therefore, who have no other, calcareous manure within reach of them but chalk,—when that is at a considerable distance, ought always to. drive it in the state of lime.—But those who are close by the pit will, in general, find.it more oeconomical to employ it in the state of chalk.
Chailf. so. much abounds ia the southern parts of Britain, that ships sometimes bring it as hallast to the north ;-^-on. which, occasions it may be purchased at a. moderate.price by the farmer.—But* although- it contains} perhaps, nearly an equal quantity of calcareous matter as the samef b$k of some very
pure pure kinds'of lime, yet it will not be good oeconomy in him to purchase it at the same price with the lime,—as at least three or four times more chalk than lime will need to be applied to his foil before it produces an equal effect. For, as it is impossible to get that hard dry chalk reduced to small enough parts, a great quantity must be applied before it can produce any sensible effect; and, although the effects of this manure aiay be lasting, yet it is never any thing nearly equal to lime, if applied in edjaal quantities.
Another calcareous matter of great utility as a manure is mark; the distinctive properties of which fall now to be considered.
Few substances appear tinder a greater diversity of forms than marle. Hence it is u
fual sual for writers on agriculture to enumerate as distinct manures the several varieties of this general class of bodies. But, as all the different kinds of marle that have hitherto been discovered may be reduced to two general classes, viz. earthy marles, which are always found in fossil strata under the earth, and Jhell marle, which always retains evident marks of its animal origin, I shall consider each of these separately, as distinct substances.
Of Earthy or Fojsil Mark.
The varieties of this class of bodies are distinguished by names, suggested by the appeararce they assume when fresh dug from their native beds. When they are soft and of an uniform texture, they are called clay marles;—when firm and hard, stone marles; —when chese assume a thin foliacious appearance, they are denominated state marles, and so on.
But, whatever appearance they assume when fresh dug, or by whatever name they are known, they all agree in this, that, if they be exposed for a sufficient time to the action of the air, they crumble into smaller parts, and fertilize the earth to which they have been properly applied.
The ingenious Dr Ainflie has demonstrated, by an accurate set of experiments, recorded in the Physical and literary essays, volume third, That all the varieties of this class of bodies contain a considerable proportion of clay, united with calcareous matter; whereas limestone, if it does not consist of pure calcareous matter, is usually united with sand in various proportions.
The calcareous matter in marle does not differ in any respect from that in limestone, and its proportions in many casses is the same in marle as in limestone,—so that the difference between the appearance and qualities of these two substances arises intirely from