Quar'rying is excavating stone, which may be done either by hand or by dynamite, blasting powder or other explosives. The art demands intimate knowledge of the structure of the rock to be excavated. This rock is commonly of one of two kinds, either stratified or igneous. The most important stratified rocks for quarrying are limestone and sandstone. The quarryman takes advantage of the bedding and natural cleavage of these rocks, so as to direct his efforts along the line of least resistance. Even some of the hardest of the igneous rocks, granite for example, have natural lines of cleavage, which may be utilized. The stratified rocks are split by means of a plug fixed in a hole in the rock between two wedges, known as "feathers." When the plug is hammered, the wedges operate on the stone with a great splitting force. This method, however, is only applicable to blocks of a limited size. Explosives, as dynamite and gunpowder, will loosen blocks of the largest description. Dynamite shatters the rock to such a degree that it is more serviceable in quarrying road-stone than building-stone. Sometimes a large block is cut off by a channeling machine, which cuts by means of a sharpened bar impelled by steam-power. When quarried, the stone is cut and dressed for use in building, statuary etc.