located nearer to the surface of the earth. As previously mentioned, Piedboeuf advances reasons deserving attention for objecting to the separation during the formation of petroleum.

Dr. Krämer is of the opinion that this process cannot be identical with the processes of distillation employed by us (distillation of coal, manufacture of gas). "Certain differences in the petroleum and the distillates of fossils presuppose a different process. It is remarkable that the oxygenous constituents, especially the phenols, which are essentially components of coal tar, are either entirely wanting in petroleum or present only in very small quantities, and that nitrogenous constituents cannot be established with certainty. Of still greater force is the fact that in all pyrogenous decompositions there is obtained besides the distillates a residue-coke remaining in the retort, while petroleum must have formed without such a residue, coal in no form having been found in localities where oil occurs." (The doubt about the absence of nitrogenous combinations has already been refuted.)

"Regarding the question of temperature at which the final transformation into petroleum has been effected, the well known experiences in dry distillation may also be referred to. We have seen that the light oils-photogen and solar oil—of brown coal tar, which is obtained at a comparatively low temperature, although much richer in aromatic hydrocarbons than even the specifically heaviest petroleum, are in this respect far behind the light oils of stone-coal tar, which chiefly consist of aromatic hydrocarbons. Now since stone-coal tar is obtained at a much. higher temperature than brown coal tar, it follows that the formation of petroleum must have been effected at a still lower temperature than is required for the production of brown coal tar. However, the lower the specific gravity of petroleum the poorer in aromatic hydrocarbons it has been found to be, and the lower it may be supposed the temperature of the formation must have been, if not, what is very likely possible, the concentration of heavy hydrocarbons took place later on. Since petroleum at a higher temperature, or when its vapors are

conducted through red-hot pipes, is decomposed to gaseous hydrocarbons, the causes of the observed differences in its composition may be reasonably attributed to a time later than its formation."

If from a chemical standpoint Dr. Krämer lays stress upon the fact that the temperature at which petroleum has been formed must have been lower than that at which brown coal distillates are produced, we have to agree with him from a geological standpoint also, though his observations are based upon the behavior of vegetable remains. Since no traces of the action of a former red heat have been found in any petroleum region, even where the oil is still in primary deposit, nor where shales which are readily reddened by heat and otherwise changed, for instance by the disappearance of the few black remains of fish scales, etc., carry or accompany oil, we are forced to the conclusion that petroleum must have been formed at a decidedly lower temperature than even the most moderate red heat. The possibility of such process of transformation at a quite low temperature is proved by O. Fraas' observations at the coral reef at Djebel Zeit, in the Red Sea. An analysis of this petroleum would be of great scientific interest.

Since the petroleum of the Carpathian fish-shale contains paraffin, though only in small quantities, and since it occurs in primary deposit which shows no sign of the action of a red heat, it follows that the formation of paraffin is also possible at a lower temperature than red heat.

The above mentioned oil, bearing fish-shale, is like the coral reef of Djebel Zeit, a proof of the possibility of petroleum being formed from animal remains at a relatively low temperature. It is also very probable that the same factors have been active in all other oil regions, the only exception being the sporadic inclusions of oil in eruptive rocks which are of no technical importance, and which may have been formed by destructive distillation of broken through coal strata.

E. Orton also arrives at the result that the transformation

1 Preliminary Report on Petroleum and Inflammable Gas, 1887, p. 11.

has taken place at a relatively lower temperature—at all events below 392° F.-and he therefore calls the process spontaneous, instead of destructive distillation.

Whether in the formation of petroleum from organisms water has co-operated is still an insolved question, which has scarcely ever been discussed.

Daubrée alone presupposes its presence necessary, his synthetic experiments having been made with the use of superheated steam. In view of the general distribution of water, especially in organisms also, its presence in the transformation. of the latter into petroleum can scarcely be doubted.

Another point in question is to what extent is it necessary to presuppose an increased pressure in the transformation of the organisms. In view of the overlying sedimentary rocks it may be supposed that the oil-bearing strata stood formerly under a greater pressure than at present. That chemical action is also. augmented by this greater pressure is well known and, hence, the formation of petroleum could be the more readily effected at a comparatively low temperature.

In the primary deposits the spheres of formation and condensation were situated in the same locality. Hence the light hydrocarbons formed could not be condensed by a lower temperature than that of their formation, their becoming liquefied being rendered possible only by standing under greater pressure, which is conditional on the degree of resistance the gases met with in their endeavor to escape, hence is dependent on the primary oil deposit being tightly closed on all sides. That petroleum in its deposits frequently stands under a high pressure has been confirmed in many localities.

G. Kraemer and W. Böttcher' also have recently arrived at the conclusion that the formation of petroleum must have taken place under great pressure.

These few observations may suffice to justify the assumption of a higher pressure in the formation of petroleum.

It is well known that the various petroleum regions yield dif

1 Ver. deutsch. chem. Ges., 1887, S. 595.

ferent crude oils, this being best illustrated by the fact that the crude oil of Pennsylvania yields 70 per cent. of illuminating oil, while that of Baku yields only about 30 per cent.

That in the same oil deposit the density of the oil decreases to a certain limit at a greater depth has been observed in many localities, and can, as previously mentioned, be explained only by the fact, that the petroleum nearer to the earth's surface has been changed and become denser by evaporation and oxidation, this also being very probably the reason why the first oil sand of Pennsylvania yields a denser crude oil than the second, and this again a denser than the third, the lowest oil sand.

In Klenczany (West Galicia) yellow petroleum, rich in paraffin, and dark petroleum, poor in paraffin and of little value, occur at a slight distance (about 3280 feet) from each other.

The difference in the oils of the various states of North America, for instance, Pennsylvania, New York, California, etc., caused Peckham to suppose for some a vegetable, and for others an animal origin, though the proofs given are not sufficient.

Dr. Kraemer1 says: "The evaporation and the superheating of the petroleum, together with a resinification taking place later on under the influence of the oxygen of the air and sulphur, are the causes of the great differences in petroleum observed at the present time. The more recent the formation of the petroleum, and the less its deposit has been changed, the more insignificant these differences appear." The latter proposition might be objected to, while the first, independent of the presupposed volcanism during these processes, mentions, in many respects, important factors of the transformation.

While Peckham seeks the difference in the material of origin, Kraemer finds it in processes acting upon the finished oil.

There is no doubt that a difference in the petroleum had to be conditional on the fact whether, for instance, remains of saurians, or of fishes, or of coralloid animals, were employed in its formation. These differences can, therefore, be sufficiently

explained by animal remains alone, without supposing, like Peckham does, entirely different materials of origin.

However, the difference in the quality of crude oil can be explained not only by the difference in the raw material and the variety of processes which have subsequently acted on the petroleum. There are other self-acting factors, such as temperature, duration of the process and the pressure prevailing thereby, the rock material which was encountered by the oil in a state of formation as already formed, which may also have co-operated in bringing about this difference in quality, as is well known to every chemist who has studied, for instance, the chemistry of coal tar. To decide in a given case to which of the above-mentioned factors the differences in quality are due, will frequently be a fruitless effort.

It may be mentioned here that coals of the same geological age and alike in nearly all other respects, for instance the coal of Wigan and of Newcastle, yield different tars, that of the first locality being rich in phenol and benzol, and that from the latter, in naphthalene and anthracene.'

3. Origin of oil deposits.

Having discussed the formation of petroleum, the next question refers to the formation of its deposits, those local accumulations by which it becomes of technical importance.

It is a fact established in various petroleum regions that petroleum may also occur in fissures. That the oil has not been formed in them, but occurs in a secondary deposit, needs no further explanation.

If the mouth of such a fissure, in which the oil ascends, is covered with debris or sand, the latter are actually filled with petroleum.

If such a fissure crosses a porous stratum, the pores of the latter will be filled with petroleum. The accumulation of oil extends with this stratum and has the appearance as if, in this

1 Dr. G. Schultz. Chemie des Steinkohlentheers, 2. Aufl., S. 22.