Although the diamond drill borings just mentioned were remarkable because of their inclination and because of the cramped quarters from which they were driven, they do not begin to compare in depth with some of the borings made in search of water and of oil. The deepest boring in the world to date is near Fairmount, West Virginia, where a hole six inches in diameter was driven to a depth of 7,579 feet or nearly a mile and a half. At that point an earth slide stopped further borings. BORING FOR OIL The time-honored method of boring for oil known as the percussive system is to hammer through the earth and rock with a heavy steel drill. The drill really consists of a long string of parts measuring altogether as much as sixty feet in length. (See Figure 64.) The drill proper or bit has a cutting edge adapted for the character of the material it is to penetrate. The bit is attached to a steel bar known as the “auger stem” which may be from twelve to forty-five feet in length. Then come the “jars” or a link member which allows a play of about sixteen inches. The purpose of this is to assist in freeing the bit from the material it is penetrating by jarring it upward on the upstroke of the drill. Above the jars there is another bar known as the sinker, and this is provided with a rope socket to which is attached the cable that carries the string of drill parts. The cable passes over a pulley to a walking beam which gives the necessary up-and-down motion. [Illustration: FIG. 64.--A STRING OF WELL-DRILLING TOOLS] The loose material in the bore is removed by a sand pump. To protect the bore from caving a casing of steel pipe must be lowered into the well. The boring may proceed at the rate of ten to sixty feet per day, depending upon the material penetrated and the depth of the well. All sorts of difficulties are liable to interrupt the work. The cable may break, the string of tools may become unscrewed, or the casing may drop into the hole, and then follows the tedious process of fishing for the lost parts and hauling them up out of the well. As the drilling proceeds, the bore becomes progressively smaller and casings of smaller diameter must be used. The well is completed by lowering a pipe within the casing through which the oil flows to the surface and is carried to the storage tanks and thence by pipe lines to the refineries. While the percussive system of drilling is very generally used throughout the American oil fields, rotary methods of drilling are largely employed in California. CHAPTER XVII FROM FIBER TO FABRIC