The sustaining power of peat moss, and peat which is sometimes found under a bed of gravel and upon a substratum of clay or marl; and bog-land varies greatly. As a rule high bog-land will bear the greater weight. The only reliable method of ascertaining its sustaining capabilities is by an actual test, and such experiments are the more requisite in unreliable soils such as mud and slake, alluvial deposits, peat and bog-land. It is known that some mossy peat and bog-land will not even resist the weight of a stone of ordinary size, but will upheave and shake upon very little pressure being applied. By draining and other consolidating operations such land may be rendered capable of sustaining a load if the weight be spread over a considerable area upon a platform of poles, timber, or fascine work, as it then as it were, floats upon the surface; but piling is not successful, as the piles disunite the particles, destroy the continuity of the layers and make a passage for water. The elasticity of bog-land is manifest even when a road-bed has become sufficiently firm and even-bearing for traffic, by the agitation of the water in any adjoining drains. In low bog-land, peat-moss, or peat-land, it is important to ascertain whether the deposit extends to a considerable depth, as in Holland it has been found that some marshes simply rest upon a bed of water, being nothing but floating peat moss, although having as great a thickness as 20 feet. It has also been noticed that marsh-lands often rest upon peat mosses with a small layer or film of loam upon them, and that they are floating masses, although the water upon which they float may not be deep; its depth may be known by the insertion of a bar or boring-tool, for when it sinks suddenly it has probably reached the water, and until its downward movement stops it shows that water exists.