In spite, however, of the outstanding differences between petroleum, oil-shales and coal, I might here point out in favour of the vegetable theory of origin, that actual petroleum and true bitumens have been found in some coals, though in small quantities, while solid paraffins have been extracted by means of pyridine and chloroform. Again, low temperature distillations have yielded petroleum hydrocarbons, all of which appear to indicate that even when coal was the overwhelming product, at certain times and places the conditions were merging into those which could yield petroleum. There is no doubt that each of the various views expressed as to the organic origin of petroleum contains elements of truth, and it is reasonable to assume that a substance so varied in its physical and chemical properties as petroleum has not in all cases been created under precisely the same conditions, or from an exactly similar source. Summing up the whole question of origin, however, the balance of opinion points to its being the result of organic action, and that the petroleum which we now find in the Palaeozoic and Tertiary rocks is substantially of the same geological age as the rocks themselves. Volumes of technological literature have been written upon this complex question of petroleum origin, and though these may be of intense interest to the student of geology, the brief references which I have already given to the question are sufficient for the purpose of this little publication. The geographical distribution of petroleum throughout the two hemispheres is no less wide than the geological. The deposits mainly occur along well-defined lines, often associated with the mountain ranges. This is chiefly due to the formation, in the elevatory process, of minor folds which have arrested and collected the oil in richly productive belts. CHAPTER II THE OIL-FIELDS OF THE WORLD Ever since petroleum and its products entered the realm of commercial commodities, there has been a ceaseless search throughout the two hemispheres for crude oil, and to-day there are comparatively few countries in the world where the presence of petroleum has not been proved. The ever-expanding uses of petroleum, which in their train have called for a continually increasing demand for crude oil, have given an impetus to the search for commercially productive oil-fields, which, in mining history, has no parallel. On the one hand, we have those important oil-producing regions which embrace enormous regions of the United States, Mexico, Russia, Roumania, the Dutch Indies, India, and Galicia; on the other, we find comparatively recent enterprise which is bringing into prominence the newer oil-producing regions of Egypt, Trinidad, Canada, the Argentine, Algeria, and various parts of Australia and Japan, though in several of these latter mentioned countries, the production of petroleum has been carried on by private means for not only many years, but even for centuries.