PETROLEUM, OR ROCK OIL. 



wells near together interfere in. the way of 

 drawing the one from the other. " It is" says 

 Prof. Evans, " one chance out of many to strike 

 oil at all, even in the neighborhoods where it 

 exists in abundance. The drill, as it enters the 

 cavity, sinks variously from four or five inches 

 to as many feet, sometimes sticking fast, as if 

 between the oblique sides of a narrow fissure. 

 But there are facts connected with the history 

 of oil wells, particularly in their intermittent 

 action, and their interference with one another, 

 which serve to show the existence, in many 

 of systems of cavities connected together 

 by channels of communication more or less 

 free, running sometimes along the strata, and 

 sometimes across them. The productiveness 

 of a well depends on its entering either one of 

 the main reservoirs, or some one of its import- 

 ant connections." 



Speaking generally, the contents of oil-con- 

 taining fissures or other cavities, and whether 

 single or communicating, will be, water at the 

 bottom, oil floating npon the water, and gas 

 filling the space above the oil, the three stand- 

 ing thus in the order of their specific gravities. 

 By natural outlets to the surface, from one or 

 other of these parts, there may result either a 

 gas or an oil spring, or one of mixed water and 

 oil. In sinking wells, a more or less vertical 

 fissure may be struck at any point, the well 

 entering the portion filled either with gas, oil, 

 or water. In the first case, gas is at first dis- 

 charged, and, if it has been subjected to great 

 pressure, with proportionate violence ; while, 

 if water from communicating crevices below 

 then rapidly enters the fissure, the oil may next 

 be forced into the lower end of the tubing and 

 be pumped out ; and later, oil and water mixed 

 will be obtained. If the well enters the part 

 of the fissure holding oil, this, by the pressure 

 of the gas above it, may be raised toward the 

 mouth of the well, or projected into the air, 

 and sometimes to a height of many feet; but 

 this action of the gas after a time becomes ex- 

 hausted; and the flow is then, of course, no 

 longer maintained. After the flow of oil from 

 such a well has ceased, and the pump is resort- 

 ed to, it is likely sooner or later to bring up a 

 mixture of oil and water. If the well directly 

 enters the water, unless the gas has sufficient 

 tension to force out the water, and then oil, 

 the latter can only be obtained by pumping out 

 so much water as, if possible, to lower the 

 water-surface to the point at which the boring 

 enters the fissure, when, usually, oil and water 

 mixed will be obtained. It is probable the 

 wells may be intermittent from several causes, 

 connected with the gradual accumulation of 

 gas, oil, or even water, in the fissures pierced ; 

 but with pumping wells the most common 

 cause must be supposed to be the time required 

 for oil to collect from surrounding porous rock, 

 or small crevices. 



Any pressure, as of gas, air, or a head of 

 water, will raise oil to a height as much greater 

 than that to which water would be raised, as. 



the specific gravity of the former is 1 . -; : /'. f.. 

 in round numbers to a height comparing with 

 that of a water column under like circumstances 

 nearly as 5 to 4. "While the oil wells thus far 

 vary in depth from 50 to near 800 feet, it is 

 stated that the deepest are as likely to raise 

 water to the surface as the shallowest. By tho 

 occurrence of rains, the production of some 

 wells is increased, while that of others, with 

 less gas, is impaired. The very large quantities 

 of oil in some cases delivered, the fact that 

 borings near together may reach oil at very 

 different depths, and other facts, go to show 

 that the somewhat popular idea of an ' ; oil 

 rock " to be reached is a mistaken one ; and, 

 although the supply of oil is sometimes, and in 

 some districts to a greater extent than in 

 others, contained in pores, or very small cavities 

 in the rock, it is more commonly doubtless 

 found in cavities of larger size, single or com- 

 municating. 



Xot only is the supply of oil, geologically 

 speaking, higher in "West Virginia and southeast- 

 ern Ohio than in the northwestern Pennsylvania 

 region ; but thus far, at least, most of the wells 

 in the former region go to much less depth 

 than in the latter. The wells in Ritchie County 

 are said to be usually from 150 to 200 feet 

 deep ; those of Bull Creek, To to 250 feet ; and 

 particular ones on and near Horse Xeck Run, 

 from 160 to 380 feet in depth. It has been sup- 

 posed that a gain in production might be se- 

 cured by sinking wells in parts of West Vir- 

 ginia to from 350 to 500 feet. In southeastern 

 Ohio the wells are usually no more than from 

 150 to 300 feet deep: but the fact that two 

 wells lately sunk, on Duck Creek and Cow 

 Run, to depths of more than 700 feet, have each 

 struck a good quality of oil, has led to the opin- 

 ion that in this region deep as well as surface 

 supplies of oil o: 



The transition from the region last consider- 

 ed to that of northwestern Pennsylvania and 

 northeastern Ohio is, in a geological point of 

 view, a transition only from the carboniferous 

 strata to some of the higher members of the 

 devonian, which lie next below. The Catskill 

 group of sandstones may be said to be confined 

 to more eastern parts of the State of Xew 

 York; and in eastern Ohio and northwestern 

 Pennsylvania, both these and the strata known 

 as carboniferous limestone are wantir_ 

 that, in the parts of the country last named, 

 the conglomerate of the coal measures comes 

 very nearly, if not in fact directly, over the 

 Chemung and Portage groups of sandstones. 

 Some beds of coal from the great Pennsylvania 

 coal-fields come out on the hill-tops some miles 

 to the southward of parts of the Alleghany 

 River along which there are now productive 

 oil wells, and some of more limited extent are 

 found on hills even in the oil region. In the 

 higher country of this region, in fact, the sur- 

 face rocks are still mostly carboniferous ; and on 

 the hills near to some of the oil-producing val- 

 leys, the conglomerate floor of the coal iiic-as- 



