W H E

The first has its name from its similitude, in appear-ance, to clay; the second from its hardness, and simili-tude to stone ; and the third from the shells, with whichit is mixed, or rather of which it is compounded.

The clay and stone marles are of the fame nature; theshell marie is very different from both. This makes itnecessary to treat of them separately.

Marie of the stone and clay kinds promotes vegetationin a surprising manner. It is probable, however, that itcontains in itself few of the principles of which the vege-table food is compounded, plants are not able to find theirfood in it. When in a bed below the surface, it resists theentrance of water, like till or clay. When near the sur-face, and turned up by the plough in great quantities, thefoil is little better than till, almost quite barren. Themethod of its operation will be best known by inquiringinto its qualities.

It is observed, that both the clay and stone marles havethe following qualities.

When long exposed to the air, or put into water, theyfall down into a powder: they are very heavy bodies: theearth of which they are compounded, is of the absorbentkind : they are attractors of acids; with them they raisea fermentation, and produce salts.

The only difference betwixt them is this: the clayMarie is sooner dissolved than the stone marie ; and com-monly has a stronger power of destroying acids, and pro-ducing salts. Dr. Home fays, that the clay marie, whichhe tried, destroyed a third more of acids than the stonemarie.

These marles seem to have much the same qualitieswith lime; and, therefore, must operate in the famemanner.

They communicate to the foil a power of attracting thevegetable food from the air, they enlarge the vegetablepasture; and they dissolve the vegetable food that is inthe foil, and prepare it for entering the roots of plants.

These marles communicate to the foil a power of at-tracting the vegetable food from the air. The absorbentearth which they contain, and the salts which they pro-duce, are strong attractors of oils.

It is observed, that they attract oils so strongly, that theyare used by some to extract greasy spots from cloaths.TVhen laid upon land, they will therefore attract oil fromthe air, which is the ingredient of the vegetable food moltWanted.

These marles enlarge the pasture of plants. They fer-ment with acids, and fall down into powder, whenexposed to the air, or put into water. These thingsmake them operate in separating the particles of the soil,With which they are mixed.

These marles also prepare the vegetable food for being'murilhment to plants. The salts which they produce,n pt only attract oils from the air, but also from the soil;dissolve these oils, and render them capable of bein gmixedWith water; and of being conveyed by it into the roots

plants.

According to some, these marles contain some oily mat-ter * This, if true, would make them operate in a man-n *r r different from lime. But this is uncertain. The earth

Which these marles are compounded, is of the absorbentfmd ; it cannot be long exposed to the air, without at-. ra &ing oils; and therefore, though they contain none inhe;r original composition, yet some marks of them maya Ppear upon trial.

W H E

These marles are long in dissolving. Large pieces ofthe-stone marie are seen sometimes undissolved, six or se-ven years after it has been laid upon land. This makesit necessary to apply a very large quantity of them, other-wise their effects will not be known.

As the quantity of marles applied is very great in pro-portion to thd quantity of lime, land, when manured withmarie, must have a stronger power of attracting the vegctable food from the air; and therefore the marie should bepreferred, when it can be as easily obtained.

As the earth of these marles is of the absorbent kind, asa great quantity of it is applied at one time, and as it islong in dissolving, it must be many years before its opera-tion ceases; and, if the land is barren, the nature of itwill be changed, and ever after, by the fame kind of dres-sings it received before, will continue to carry better crops.In this respect also it is preferable to lime. This advantage,however, depends, in a great measure, upon the nature of:the soil. If the soil is soft and spungy, and has not a firmbottom, the marie, by its weight, will, by degrees, pene-trate, like lime, beyond the reach of the plough; andtherefore, must leave the soil no better than it found it.

Although, in some respects, these marles seem prefer-able to lime, yet we are to consider, that their principal.,operation is the fame with that of lime; which is enlarg-ing the pasture of plants, and sitting the vegetable food forentering their roots. When land, therefore, manured witss,them, is exhausted by crops, it cannot receive much bene-fit from them a second time, if immediately applied. Thisis confirmed, it is said, by experience. It is observed, thatmarie, when applied a second time to land exhausted bycrops, has not the fame effect as when first applied.

As marie operates in the fame manner as lime, it fol-lows likewise, that limed land exhausted by crops, can re-ceive little benefit from the application of marie; and thatmarled land, exhausted by crops can receive little benefitfrom the application of lime. As it exhausts the vegeta-ble food, the proper manure after it is dung, which con-tains this food in the greatest plenty.

It was observed, that marie operates chiefly by attractingoils and acids from the air; the longer, therefore, that itlies upon land, exposed to the influence of the air, the morequickly it will operate.

The difference betwixt the clay and stone marles wassaid to consist in this: that the clay marie dissolves sooner,and has a stronger power to destroy acids and produce salts.This kind is therefore preferable, as a less quantity wiiiproduce the fame effects. If Dr. Home’s experiments areto be’depended upon, ot rather, if all clay and stone marleshave the fame powers with those which he made his ex-periments with, then four cart-load of the clay marie is-equal to five of the stone.

What was said of lime, with respect to the applicationof it in smaller and larger quantities, may likewise be saidof marie. When barren land is to be improved, the marieshould be laid on in large quantities: but when land is ingood order, the applying a fifth or sixth part of the quan-tity commonly used, once in six or seven years, may havevery good effects.

Shell marie is very different in its nature from the othertwo. It is commonly classed among the animal manures.

It does not dissolve with water, as the other marles do.It socks it up, and swells with it, like a fpunge. It is amuch stronger attractor of acids than they. Dr. Homefays, that it takes six times more of acids to saturate it than4 Q, any