clay and shale beds in cuttings are present, a slope of 1½ to 1 has been insufficient, and they have not been stable till an inclination of 2 to 1 has been adopted. As cuttings in rock are frequently in the side of a hill, the dip of the strata should be ascertained, and in the case of an unstratified rock, it should be known whether it is fissured or lies upon a solid and firm bed considerably below the level of a cutting, so that it may be prevented from movement. It should also be ascertained if the top stratum is a mere crust, such as a capping of conglomerate resting upon clay-rock, through which water may burst and cause it to separate, and sometimes the rock may be more solid in the valleys than upon the hill-side because of greater diluvial action, and induration caused by exposure. The crystalline rocks are the least easily destroyed and are generally rough and jagged. The science of geology shows that limestones, sandstones and clays, were originally heaps of mud deposited, removed or arranged by water; and that boulders are transplanted masses from the parent rock, and are worn and rounded by mechanical attrition. Consideration of the manner in which rocks have been formed affords a fair indication of their stability in earthwork; for instance, many clay rocks are reduced to a pasty condition by the action of water and air, but with different results according to their nature, some requiring blasting to excavate them. On the other hand, there are sandstones which although soft in the quarry become hardened when exposed to the atmosphere. A dock cut in red sandstone when exposed to the atmosphere may slip and fail, but if the rock be protected from the weather or constantly covered with water it may be reliable.