Aside from the path levels, building begins with the rocks, not with the soil. This is a highly important point. Place the boulders first; they are the big effects. Aside from that, the heaviest work will be out of the way. Then start in with the outlining base rocks. These should be placed with the largest surface to the ground and should vary in size. It is not essential that the lowest rocks should
be slightly buried in the ground, but that course is preferable.
When the paths and outer margins have been thus defined, scatter more rocks over the intervening surface, placing them fairly thick but not close together. Next, fill in with soil, packing it firmly and ramming it hard into every crevice. If it fits in with the day's work, it is not a bad plan to water the rock work well in order to pack the soil, and when resuming the labor on the morrow, to add more soil, well pressed down, before proceeding with the second layer of rock.
This second layer should have the rocks placed with the front edge slightly back from that of the lower row in order to form a slope, though an occasional overhang may be fashioned if required for a certain plant known to abhor a drip from above. The construction then proceeds
as before, until the desired height is reached. The height is entirely arbitrary, but some points should be at least as high as the line of vision, as one of the great advantages of a rock garden is the pleasure of enjoying some of the typical rock plants without stooping. The rocks used as fillers should overlap here and there to give strength, but care must be taken to contrive plenty of long soil runs. Eighteen inches should be the very least. A plant like the alpine androsace is a tiny rosette, seemingly requiring no more than an inch or two of soil, but its roots are likely to be found following an earth-filled crevice in the rocks to the depth of a yard or so. It is because of this deep penetration of roots that the soil should be packed so very firm; the roots must be in no danger of loose soil or of striking a hidden hollow.
Where a rock would bear too heavily on the one below it, even with soil between, the pressure may be relieved by the use of small stones. The soil run need not be straight, but it must be continuous, so that the roots of the plant may find their way from A through to B
At no point between two stones should the layer of soil be less than two or three inches thick after being packed hard. If an upper stone is likely to bear down too heavily and crush the plant roots, this may be avoided by placing small stones here and there in the layer of soil. The roots will work between these stones, but there must be a continuous, though not necessarily straight, soil run from the front of the rock work to the solid filling