confines himself to the regions known to have produced oil, but the selection of the particular location for a well within these limits appears to be eminently fanciful.  The more scientific generally select a spot either on the anticlinal or synclinal axis of the formation, giving preference to the former position.  Almost all rock formations have some inclination to the horizon, and the constant change of this inclination produces a series of waves, the crests of which are known as anticlines, and the troughs as synclines.  Many drillers suppose that the gas seeks the anticlines and the oil the synclines, but others, equally long-headed, discard entirely all theory of this kind, and drill wherever it may be most convenient or where other operators have already demonstrated the existence of gas.  It will surprise many of our readers to know that the divining rod, that superstitious relic of the middle ages, is still frequently called upon to relieve the operator of the trouble of a rational decision.  The site having been selected, the ordinary oil-drilling outfit is employed to sink a hole of about six inches in diameter until the gas is reached.  In the neighborhood of Pittsburgh, this is usually found at a depth of 1,300 to 1,500 feet, in what is known as the Third Oil Sand, a sandstone of the Devonian period.  Where the gas comes from originally is an open question.  When the driller strikes gas, he is not left in any doubt of the event, for if the well be one of any strength, the gas manifests itself by sending the drill and its attachments into the air, often to a height of a hundred feet or more.  The most prolific wells are appropriately called “roarers.”  During the progress of the drilling, the well is lined with iron piping.  Occasionally this is also blown out, but as a rule the gas satisfies itself with ejecting the drill.  When the first rush of gas has thrown everything movable out of its way, the workmen can approach, and chain the giant to his work.  The plant at the well is much simpler than one would suppose.  An elbow joint connects the projecting end of the well piping with a pipe leading to a strong sheet-iron tank.  This collects the salt water brought up with the gas.  Ordinarily, about half a barrel accumulates in twenty four hours.  A safety valve, a pressure indicator, and a blow-off complete the outfit.  When the pressure exceeds a prescribed limit, the valve opens, and the gas escapes into the blow-off.  This is usually 30 feet high or more, and the gas issuing from the top is either ignited or permitted to escape into the atmosphere.  The pipe line leading from the tank to the city is of course placed underground.  Beyond a little wooden house, the blow-off, and a derrick, the gas farms differ little in appearance from those producing less valuable crops.  The pressure of the gas at the wells varies considerably.  It is generally between 100 and 325 pounds.  As much as 750 pounds per square inch has been measured, and in many cases the actual