These gases always exist in a high state of tension, since this accumulation has been gradual and almost irresistible. In many cases, when struck by the auger and thus relieved, they have rushed forth from the well with the violence of exploded gunpowder, and have ejected the ponderous boring-tools out of the hole and to great distances from the spot. It is thus manifest that the pressure of the confined gases on the oil must be very great; and when the auger descends into an oil-cavity, without first striking its communicating gas, the pressure on the oil must cause it to rush up the auger-hole with great violence. But, if the gas be first cut in large quantities, of course it will flow up the hole independent of the oil. In case the hole is then continued into the oil, it will depend on the equilibrium of pressure: that is, if the gas forces its way through the vent first made by the auger with more violence than it bears on the oil, little or no flow will occur; but if the pressure be nearly on equilibrium, the flow will be intermittent. If the gas escapes through the upper or first vent, so as to relieve its pressure on the oil, then what oil may be struck must be pumped. If both oil and gas exist in small quantities, and the pressure or tension is, in consequence, weak, then pumps must also be used to obtain the oil.
Figure 190 illustrates both gas and flowing wells, when both exist in the same formation ; but at a great depth gas alone is found, independent of petroleum; and figure 191 illustrates this.
In its horizon or position gas occupies a higher stratum than oil, when both exist together, but when gas exists independent of petroleum, its geological horizon is found at a much greater depth and in a still greater state of tension, and when struck rushes forth with still greater violence, as demonstrated by the terrific outburst of gas from the deep wells on the Great Ka nawha. But the great pressure of this deep gas forces small quantities of its most volatile parts through the minute crevices of the rocks to the sur face, and if cavities are found in any slaty strata reservoirs of oil are formed, which constitute the upper or heavy oils of Kanawha. It may seem strange that so light a gas should form this heavy oil, but it is produced on the same principle on which all heavy oils are produced, viz.: by the condensation of the gas and the escape of its most volatile parts. The carbon which constitutes from one-third to one-half the volume of this light gas has little or no affinity for hydrogen when in a cold condition : therefore the carbon condenses or separates from a portion of the hydrogen, leaving it free, and the result is a carbon oil, containing 85 carbon and 15 hydrogen. A further evaporation of the hydrogen leaves the carbon in all stages of density, from a heavy oil to bitumen and coal.