Professor White goes on to say: "After visiting all the great gas-wells that had been struck in western Pennsylvania and West Virginia, and carefully examining the geological surroundings of each, I found that every one of them was situated either directly on or near the crown of an anticlinal axis, while wells that had been bored in the synclines on either side, furnished little or no gas, but in many cases large quantities of salt water. Further observation showed that the gas-wells were confined to a narrow belt, only one-fourth to one mile wide, along the crests of the anticlinal folds. These facts seem to connect gas territory unmistakably with the disturbance in the rocks caused by their upheaval into arches, but the crucial test was yet to be made in the actual location of good gas territory on this theory. During the last two years, I have submitted it to all manner of tests, both in locating and condemning gas-territory, and the general result has been to confirm the anticlinal theory beyond a reasonable doubt. "But while we can state with confidence that all great gas-wells are found on the anticlinal axes, the converse of this is not true, viz., that great gas-wells may be found on all anticlinals. In a theory of this kind, the limitations become quite as important as, or even more so, than the theory itself; and hence, I have given considerable thought to this side of the question, having formulated them with three or four general rules, which include practically all the limitations known to me up to the present time, that should be placed on the statement that large gas-wells may be obtained on anticlinal folds, viz.: "(a) The arch in the rocks must be one of considerable magnitude. (b) A coarse or porous sandstone of considerable thickness, or, if a fine-grained rock, one that would have extensive fissures and thus, in either case, rendered capable of acting as a reservoir for the gas, must underlie the surface at a depth of several hundred feet (500 to 2,500 feet). Probably very few or none of the grand arches along mountain ranges will be found holding gas in large quantity, since in such cases the disturbance of the stratification has been so profound that all the natural gas generated in the past would long ago have escaped into the air through fissures that traverse all the beds. Another limitation might possibly be added, which would confine the area where great gas flows may be obtained to those underlaid by a considerable thickness of bituminous shale. "Very fair gas-wells may also be obtained for a considerable distance down the slope from the crest of the anticlinals, provided the dip be sufficiently rapid, and especially if it be irregular or interrupted with slight crumples. And even in regions where there are no marked anticlinals, if the dip be somewhat rapid and irregular, rather large gas-wells may occasionally be found, if all other conditions are favorable." (Science, June 26, 1885.) To some of these statements, Mr. C. A. Ashburner, Geologist, in charge of the Second Pennsylvania Geological Survey, took exceptions, in a letter published in Science, July, 1885. He says: "Professor White's theory that 'all great gas-wells are found on the anticlinal axes,' cannot be accepted, until he shall limit, by definition, all great gas-wells to exclude all gas-wells, both large and small, comparatively, which produce gas from strata not found either on anticlinal axes or in close proximity to such structural lines. The Kane gas-wells, the Ridgway well, the 'Old Mullin Snorter,' and several Bolivar wells are notable instances among many which might be mentioned, where large gas-wells have been drilled in or near the center of synclines. "Although it is a fact that many of our largest Pennsylvania gas-wells are located near anticlinal axes, yet the position in which gas may be found, and the amount to be obtained, depend upon (a) the porosity and homogeneousness of the sandstone which serves as a reservoir to hold the gas, (b) the extent to which the strata above or below the gas-sand are cracked; (c) the dip of the gas-sand and the position of the anticlines and synclines; (d) the relative positions of water, oil and gas, contained in the sand; and (e) the pressure under which gas exists before being tapped by wells." To these criticisms Professor White makes reply, by urging that subordinate anticlinals often run along the central line of synclines, and that when gas is found in synclines it is at these points, and that when found here, it is seldom free from salt-water by which it is likely to be overpowered. He further urges that all the successful gas companies of western Pennsylvania and West Virginia are getting their gas from the crests of anticlinal axes, while those that have confined their operations to synclines, have met with uniform financial disaster. He points to the brilliant lights along the summits of the eight axes nearest to Pittsburgh, and he has since added a ninth, and also to the darkness that envelops the intervening synclines, in which hundreds of thousands of dollars have been invested without developing a single profitable gaswell. To the qualifications already made, Professor White would probably add, at this time, one to the effect that gas-wells shall be located on the domes of the axis, rather than its depressions, recognizing the same line of facts in regard to them that Minshall had already established in the case of the White Oak anticlinal of Ohio and West Virginia, to which reference has previously been made. The facts cited by Professor White as to the gas-supply of Pittsburgh, seem conclusive. Every foot of it comes from anticlinals, but not from them because it has been sought nowhere else, but because, if found in other stations it is speedily overcome and extinguished by salt-water. Where anticlinals of the type here referred to traverse an oil-bearing series, it may be considered demonstrated that they exert a decided effect on the accumulations of oil and gas in this series. So rational is such a conclusion, so directly does it result from the facts already stated, that it is hard to see on what grounds it can be called in question. While there is no element of the theory, as stated by Professor White, that differs from the theory as heretofore stated, his applications are bold, original, and, best of all, successful, and they mark a new period in our study of the geology of oil and gas. of it But as has been already shown, anticlinals are of infrequent occurrence in Ohio. A few of the low arches of western Pennsylvania extend across the border, but they soon flatten out and disappear. Even if anticlinals are held to account for the facts of oil and gas accumulation, the theory would have but limited application to our geology. Though distinct arches are for the most part wanting in our geology, there is another sort of structural deformation found here, which is connected in a direct way with the oil and gas of eastern Ohio. The structure referred to is associated with the arrest or suppression of the prevailing dip of the rocks for a given space and the establishment of a terrace or level bench in its place. If the series had lain level instead of being inclined at the slight angle which marks most of eastern Ohio, the movement to which the present terrace is due would have resulted in a low arch, but the uplifting force was too feeble to do more than counteract for a short space the normal dip by which the entire series is affected. The structure referred to comes out to view in the Macksburg oil field, and is represented in the maps and sections that accompany the report upon this field. The entire series that is found to be connected here with oil production is at least 1,500 feet thick. It enters the field dipping gently to the southeast, at the rate of twenty to thirty feet to the mile, but it suddenly ceases its descent, and for about three miles there is no appreciable fall. In other words, a normal descent of sixty to seventy-five feet is neutralized. The amount of territory included in the terrace appears to be fifteen to twenty square miles. Beyond this, the regular dip is resumed. In the 1,500 feet of rock which compose the section that the wells here penetrate, there are not less than five distinct oil-sands, or in other words, five horizons at which oil and gas are sometimes found. Each one of these is productive of oil to a greater or less degree, upon the terrace, and of gas, upon the upper margin of the terrace. The development of the field began with the discovery of oil in the shallowest sand. Step by step the lower horizons were reached. The productive areas of each have the same surface boundaries. The petroleum contained in the different sandstones has different characters, varying in gravity, in color, in chemical properties, from sand to sand. Wells are in operation in most if not in all of these horizons in the Macksburg field at the present time. How are these facts to be explained? If there were an anticlinal fold here, it could be urged that the gas had found its way through the fractures and fissures of the arch from the bottom upward, so that one supply could account for charging all of the rocks. This explanation would leave the differences in quality of the oils found in the several rocks unexplained, it is true, but it might still be maintained. There is, however, neither arch nor fold of any sort. That five sand-rocks distributed through 1,500 feet of stratified deposits, should each happen to secure the right grain and composition to make them repositories of oil, within exactly the same geographical limits, is of course incredible. There is but one explanation of the facts here given. The accumulation of oil and gas is due to the structure, the arrangement, of the rocks concerned. In other words, structure is a vital element in the accumulation of oil and gas. The facts in eastern Ohio point to the conclusion that all other conditions for oil-production are met much oftener than the structural conditions required. The source of gas on the large scale is found in the universal sheet of shale that underlies this portion of the state. A reservoir is furnished by the Berea grit, almost as wide as this universal source of gas. The Cuyahoga shale has everywhere the essential conditions for roof or cover of the oil-sand. But all of these are powerless to produce an oil field until the right inclination is given to the series. This condition is met in but few instances, so far as our present knowledge is concerned. The Wellsburg gas field in the Ohio Valley below Steubenville has a structure similar to the Macksburg field. There is a similar arrest of normal dip and a consequent terrace-like bench upon the summit of which the gas is found. Oil has not yet been reported from this field, but if explorations are continued it will undoubtedly be found. Accurate measurements have not yet been applied to all of the few oil fields and gas fields of eastern Ohio, but so far as examination has gone every one of them betrays structural irregularity, and most of them point to the terrace-like structure already described. The true character of the Macksburg field was first suspected and approximately determined by Mr. F. W. Minshall, but no instrumental measurements, other than barometrical, were employed until those that are recorded in a subsequent chapter of this report. By connecting the levels of the coals and limestones of the outcrop with the positions of the several oil-sands, as shown in the drill-holes, it is seen that the entire series has risen and fallen together, and that conclusions as to the depth of the lowest stratum reached, can be safely grounded on the elevation of those that are shown in the hill-sides. d. Structural Irregularities in Northwestern Ohio. The occurrence of petroleum and gas, but especially of the latter, in northwestern Ohio, has been found to be associated with greater irregularities of structure than are known elsewhere in the state, except in a single locality. The drift deposits of this region are so thick and 80 continuous that there are no adequate opportunities to determine the horizons or dip of the underlying rocks by natural outcrops, and inasmuch as the surface does not betray any notable irregularity, it has been a great surprise to find, from the well-records, that the strata are dipping at some points at the rate of 300 feet to the mile. It is in Findlay that the most marked disturbance occurs, and the great supplies of gas that are found there appear to be closely connected with this disturbance. The largest gas-well is located near the edge of a steep descent, while others that are situated on the slopes yield both gas and oil. The wells at the bottom of the slope have yielded thus far oil alone, or oil and salt-water. The facts connected with this irregularity of structure will be fully stated in a succeeding chapter. It is only necessary to state, at this point, that the gas of western Ohio, like that of the eastern half of the state, seems to depend upon unusual facts of structure for all of its important accumulations. C. ROCK-PRESSURE OF GAS. In connection with the modes of accumulation of gas in its rock reservoirs that have been already discussed, we come upon another topic of considerable scientific and practical interest, viz., the pressure exerted by the gas upon the rock in which it is contained. The only means that we have of ascertaining this pressure is by drilling into the gas-rock. The pipe that connects this reservoir with the surface will, when closed, contain gas in the same state of tension that exists in the rock. The pressure is determined by a steam guage attached to the pipe. It is known as the rock-pressure or closed pressure of the well, and it ranges in amount from one to one thousand pounds to the square inch. In all the great gas-fields that are in process of exploitation, the rock-pressure ranges from 300 to 750 pounds, and beyond the latter figure it very seldom rises. In shale gas-wells the pressure seldom rises to 100 pounds, the ordinary range being between twenty-five and seventyfive pounds. The open pressure of a well, on the other hand, is the pressure exerted by the column of gas escaping with unobstructed flow from the well. It is registered by a guage of some sort that is held in the current. The amount of open pressure depends upon two factors, viz., the volume of gas discharged in a given time, and the size of the orifice through which it is discharged. The first element is not under our control, but by varying the size of the pipe, we find very different results. The smallest figure are, of course, obtained when the gas is escaping through the casing, or the 55-inch pipe with which wells are commonly supplied. It requires a |