The old Eastern method of drilling has obviously been the forerunner of the Canadian, standard, and other systems of to-day, the wire rope replacing the use of poles. In oil-field work, the principal types of percussion drills used are known (1) as the Pennsylvanian cable, (2) the Canadian pole, and (3) the Russian free-fall system, and though from time to time many attempts have been made to introduce modifications of these, the vast majority have been unsuccessful in their operation. The Pennsylvanian cable system was used for drilling the earliest oil-wells in the United States, and doubtless took its name from the fact that it was so largely used in that oil region. As may also be gathered from the name, the principal feature in this system is the cable by which the tools are suspended and connected to the walking beam. There is no doubt that this system of drilling, which has been so universally used in the oil-fields, gives most satisfactory results. When first introduced in Pennsylvania, the cable system of drilling was particularly simple, and did remarkably good work, for the reason that the strata usually encountered was of such a nature that it did not cave, and, as a result, the well-pipe was only lowered when the full depth of that string had been drilled. The drilling bits were seldom more than 4 inches thick. In order to give a rotary motion to the bit, the continuous twisting of the cable to and fro was necessary; but when in other fields, where deeper strata had to be explored, the cable system was introduced, the semi-sandy nature of the strata called for wells of larger diameter with correspondingly larger drilling bits. As a consequence of the additional weight of the drilling bit, it was found that the swing of the tools was sufficient to give them a rotating movement for the drilling of a circular hole. In regions where caving-in of the walls of the wells was liable to occur, the string of pipe had to closely follow the tools, which, with the old Pennsylvanian type of rig, meant frequent winding of the cable from the bull wheel, so as to allow of the well pipes being handled. In order to prevent the waste of time which these operations occasioned, the calf wheel was added, by means of which the pipe could be lowered into the hole without the removal of the drilling cable. This cable almost invariably was of the Manila character, and in many instances this rope is retained to-day, though wire ropes have been introduced frequently.