For statuary, and "undercut" work generally, an elastic mould - of glue and treacle (80: 20 parts) - may be used; the mould, when set, is waterproofed by immersion in a solution of potassium bichromate followed by exposure to sunlight, or in some other way.
It is made sufficiently strong to bear the weight of the animals, which are confined within their bounds by undercut overhanging ridges, and by deep and wide ditches, masked by rockwork.
On the east it is strongly undercut by the retrogressive erosion of the headwaters of the Red, Brazos and Colorado rivers of Texas, and presents a ragged escarpment, 500 to 800 ft.