Petroleum is found to a greater or less degree in almost every country of the world ; in fact, if the gaseous and solid forms of bitumen are consid ered as indications of the presence of petroleum, it must immediately be pronounced one of the most widely distributed of all natural substances. It also occurs in almost all ages of rocks, though the deposits which have become commercially impor tant so far have been confined mainly to unaltered rock formations of special periods. The popular impression that petroleum is an unusual substance in nature is entirely without foundation ; it only the valuable accumulations of oil which are more or less scattered.
All the world over, attention has first been at tracted to the existence of petroleum by the so called " surface indications," such as the appear ance of oil bubbles in wells and springs, or a scum of oil floating on the surface of ponds and streams. In the face of almost total ignorance, both as to the true nature of the oil and general underground conditions, it was perhaps only natural to believe that the petroleum came from " subterranean reservoirs," " underground lakes," or " flowing streams of oil." This early belief was materially strengthened by the drilling of unproductive wells, and by the practical independence of many of the Russian wells, despite the fact that they were lo cated relatively close together. It was supposed that non-productive wells had failed to penetrate an oil-filled cavity in the rock, while the great pro ducers were those which happened to strike unusu ally large cavities or the intersection of two fissures or channels. The early accounts of petroleum wells are full of rude illustrations of such im aginary underground caverns of fantastic shape, with gas above, petroleum in the center, and water below.
Caverns and fissures may exist in the rocks be neath the surface, but the records of hundreds of thousands of wells sunk in all parts of the world do not show that petroleum deposits are necessa rily associated with them. On the contrary, the drills indicate beyond question that the oil comes from porous rock formations and not from appre ciable openings in the strata. It comes from the multitude of tiny spaces between the grains of the rock itself instead of from one big chamber or series of connecting chambers.
The first operators in the petroleum industry in this country also argued that the appearance of oil on the surface of streams indicated the exist ence of a reservoir near by, and they came to be lieve that the accumulations of petroleum under ground coincided with depressions or valleys on the surface. The river flats, moreover, offered bet ter sites for operations than did the steep slopes of neighboring hillsides, so that for a time efforts to secure oil were confined to the valleys. But the spread of operations from one place to another soon demonstrated that the oil-producing forma tions were of greater extent than had been im agined. Then the more far-sighted operators, or
perhaps the more reckless, began to doubt that the productive area necessarily underlay the river bottoms, and to wonder if the neighboring uplands did not also cover the hidden treasure. With this class of men, to wonder was to act. Despite the derisive name, " wildcat " applied to their ven tures, many sunk wells on the uplands adjoining the productive valleys, and proved that the oil rocks could be reached. Wildcat operations there by became a regular part of the oil business, serv ing in later years to mark the limits of old, and to locate new, oil-producing territory.
In most cases there is a comparatively large area which can be called an " oil field," the limits of which may be quite closely determined from a study of the rock formation, and by sinking an occasional test well. Within the main field there are usually several distinct areas, or " pools," from which the chief production comes, for it is very unusual to find oil in paying quantities in every part of a field. " Pools " are usually dis covered through surface indications or " wildcat ting," though the attitude and character of the rocks may be some guide. Individual pools vary from a few acres to several hundred square miles, while the main field in which they occur may in clude thousands of square miles. The famous Spindle Top pool in Texas covered scarcely 300 acres, while the great Appalachian field covers nearly 50,000 square miles and includes a score of important pools.
The discovery of enormous quantities of petro leum far removed from coal-bearing rocks natu rally led to much speculation concerning its origin, since it could no longer be regarded as having a common origin with coal. In accordance with the idea of occurrence in underground chambers, it was supposed by many that the interior of the earth contained " an enormous reservoir of liquid petroleum," from which it was injected into the fissures above. This explanation was supported by the amusing argument that " petroleum could not have come from the clouds." Another theory attempted to explain petroleum deposits as a result of volcanic action, in spite of the fact that many of the most important localities showed no signs of volcanic activity either past or present. A third hypothesis sought to include the action of the salt in the salt water which is almost universally found in association with petroleum. Another thought that petroleum was formed by the interior heat of the earth acting on the tur pentine of pine trees. But of all the curious the ories, propounded at one time or another, the most absurd is undoubtedly found in the idea of a Penn sylvania oil man, who believed that American petroleum was the urine of whales which had found its way from the Arctic region through sub terranean passages.