water to rife upwards, forming fprings, bogs, and the other phaenomena of this nature; which being variously diverfified in different circumstances, produce that variety of appearances in this refpect that we often meet with.

This being the cafe, we may naturally conclude, that an abundant fpring need never be expected in any country that is covered to a great depth with fand, without any ftratum of clay to force it upwards, as is the cafe in the fandy deferts of Arabia, and the immeasurable plains of Lybia : Neither are we to expect abundant fprings in any foil that confifts of an uniform bed of clay from the surface to a great depth. For, it must always be in fome porous ftratum, that the water flows in abundance, and it can be made to flow horizontally in that, only when it is fupported by a ftratum of clay, or other fubftance that is equally impermeable by water. Hence the rationale

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of that rule fo universally established in digging for wells, that, if you begin with fand or gravel, &c. you need feldom hope to find water till you come to clay; and, if you begin with clay, you can hope for none in abundance, till you meet with fand, gravel, or rock.

It is neceffary that the farmer should attend to this procefs of nature with care, as his fuccefs in draining bogs, and every species of damp and fpouting ground, will in a great measure depend upon his thorough knowledge of this, his acuteness in perceiving, in every cafe, the variations that may be occafioned by particular circumftances, and his skill in varying the plan of his operations according to these. As the variety of cafes that may occur in this refpect is very great, it would be a tedious talk to enumerate the whole, and describe the particular method of treating each. I fhall, therefore, content myfelf with enumerating a few

par

particular cafes, to fhow in what manner the principles above established may be applied to practice.

Let Fig. 21ft reprefent a perpendicular section of a part of the earth, in which AB is the surface of the ground, beneath which are several strata of porous fubftances which allow the water to fink through them till it reaches the line CD, that is supposed to reprefent the upper furface of a folid bed of clay; above which lies a ftratum of rock, fand, or gravel. In this cafe, it is plain that, when the water reaches the bed of clay, and can fink no farther, it must be there accumulated into a body; and, feeking for itself a paffage, it will flow along the surface of the clay, among the fand or gravel, from D towards C; till at laft it iffues forth, at the opening A, a fpring of pure water.

If the quantity of water that is accumulated between D and C is not very confiderable, and the ftratum of clay approaches

near

near the furface, in that cafe, the whole of it will iffue by the opening at A, and the ground will remain dry both above and below it. But, if the quantity of water is fo great as to raise it to a confiderable height in the bed of fand or gravel, and if that ftratum of fand is not difcontinued before it reaches the furface of the ground, the water, in this cafe, would not only iffue at A, but would likewife ooze out in fmall ftreams through every part of the ground between A and a; forming a barren patch of wet fandy or gravelly ground upon the fide of a declivity: Which is a phaenomenon that every attentive obferver must have frequently met with.

To drain a piece of ground in this fituation is, perhaps, the most unprofitable task that a farmer can engage in; not only because it is difficult to execute, but also, because the foil that is gained is but of very little value. However, it is lucky that patches

patches of this kind are feldom of great breadth, although they fometimes run along the fide of a declivity, in a horizontal direction, for a great length.

The only effectual method of draining this kind of ground is, to open a ditch as high up as the highest of the springs at a, which should be of fuch a depth as not only to penetrate through the whole bed of fand or gravel, but alfo, to fink fo far into the bed of clay below, as to make a canal therein fufficiently large to contain and carry off the whole of the water. Such a ditch is represented by the doted lines a, e, z; but, as the expence of making a ditch of fuch a depth as this would suppose, and of keeping it afterwards in repair, is very great, it is but in very few cafes that this mode of draining would be advifeable; and never, unless where the declivity happens to be fo fmall, that a great furtace is loft for little depth; as would have happened here, if the

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