The shape of ground must be either a convex, a concave, or a plane; in terms less technical called a swell, a hollow, and a level. By combinations of these are formed all the irregularities of which ground is capable; and the beauty of it depends on the degrees and the proportions in which they are blended.

Both the convex and the concave are forms in themselves of more variety, and may therefore be admitted to a greater extent than a plane; but levels are not totally inadmissible. The preference unjustly shewn to them in the old gardens, where they prevailed almost in exclusion of every other form, has raised a prejudice against them. It is frequently reckoned an excellence in a piece of made ground, that every the least part of it is uneven; but then it wants one of the three great varieties of ground, which may sometimes be intermixed with the other two. A gentle concave declivity falls and spreads easily on a flat; the channels between several swells degenerate into mere gutters, if some breadth be not given to the bottoms by flattening them; and in many other instances, small portions of an inclined or horizontal plane may be introduced into an irregular composition. Care only must be taken to keep them down as subordinate parts, and not to suffer them to become principal.

There are, however, occasions on which a plane may be principal: a hanging level often produces effects not otherwise attainable. A large dead flat, indeed, raises no other idea than of satiety: the eye finds no amusement, no repose on such a level: it is fatigued, unless timely relieved by an adequate termination; and the strength of that termination will compensate for its distance. A very wide plain, at the foot of a mountain, is less tedious than one of much less compass, surrounded only by hillocks. A flat therefore of considerable extent may be hazarded in a garden, provided the boundaries also be considerable in proportion; and if, in addition to their importance, they become still more interesting by their beauty, then the facility and distinctness with which they are seen over a flat, make the whole an agreable composition.