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
