1216. Mechanical consolidation will improve some soils, such as spongy peats and light dusty sands. It is but a limited source of improvement, but still it deserves to be noticed. The proper degree of adhesiveness is best given to loose soils by the addition of earthy matters; but mere rolling and treading are not to be altogether rejected. To be benefited by rolling, a soil must be dry, and the operation must not be carried too far. A peat-bog drained and rolled will sooner become covered with grasses than one equally well drained and left to itself. Drifting sands may be well rolled when wet, and by repeating the process after rains they will, in time, acquire a surface of grass or herbage. Every cultivator knows the advantages of rolling light soils after sowing. Gardeners tread in seeds on certain soils, and roll grass lawns to improve the quality of the turf.