have criticised Newberry's theory have, in all instances, counted destructive distillation as involved.

C. Statement of Peckham's Distillation Theory.

There is, however, another statement of the distillation theory that must be briefly considered. It is that of Peckham. It is clear and self-consistent, recognizing all the necessary factors and conditions. He refers the oil and gas of Pennsylvania, and adjacent territory, to a distillation effected by the heat that accompanied the elevation of the Appalachian mountain system. He says (Census Reports X, 70):

"Bitumens are not the product of the high temperatures and violent action of volcanoes, but of the slow and gentle changes at low temperature, due to metamorphic action upon strata buried at immense depths. . . It is not neces

sary here to discuss the nature or origin of metamorphic action. It is sufficient for our purpose to know that from the Upper Silurian to the close of the Carboniferous periods, the currents of the primeval ocean were transporting sediments from northeast to southwest, sorting them into gravel, sand and clay, forming gravel bars and great sand-beds beneath the riffles, and clay-banks in still water, burying vast accumulations of sea-weeds and sea-animals far beneath the surface. The alteration, due to the combined action of heat, steam and pressure that involved the formations of the Appalachian system from Point Gaspe, in Canada, to Lookout Mountain, in Tennessee, involving the Carboniferous and earlier strata, distorting and folding them, and converting the coal into anthracite, and the clays into crystalline schists, along their eastern border, could not have ceased to act westward along an arbitrary line, but must have gradually died out farther and farther from the surface.

"The great beds of shale and limestone containing fucoids, animal remains and even indigenous petroleum, must have been invaded by this heat action to a greater or less degree.

"Too little is known about petroleum at this time to enable any one to explain all the phenomena attending its occurrence on any hypothesis, but it seems to me that the different varieties of petroleum are the products of fractional distillation, and one of the strongest proofs of this hypothesis is found in the large content of paraffine in the Bradford oil, under the enormous pressure to which it is subjected.

"If this hypothesis really represents the operations of nature, then we must seek the evidences of heat action at a depth far below the unaltered rocks in which the petroleum is now stored."

The statements now presented, inadequate and unfinished as they appear, are probably the most careful and extended that have been made upon the subject. They bring before us two main views as to the origin of petroleum, viz.:

(1) Petroleum is produced by the primary decomposition of organic matter, and mainly in the rocks that contained the organic matter. Of this view, Hunt is one of the chief advocates.

(2) Petroleum results from the distillation of organic hydrocarbons

contained in the rocks, and has generally been transferred to strata higher than those in which it was formed. Newberry and Peckham have been quoted at length in support of this general theory. Newberry holds that a slow and constant distillation is in progress at low temperatures. Peckham refers the distillation of the petroleum of the great American fields to the heat connected with the elevation and metamorphism of the Appalachian mountain system.

These three views as to the date of the origin of petroleum and gas are seen to cover almost all of the possibilities in regard to the subject. Hunt believes petroleum to have been produced at the time that the rocks that contain it were formed, once for all. Newberry believes it to have been in process of formation, slowly and constantly, since the strata were deposited. Peckham refers it to a definite but distant time in the past, but long subsequent to the formation of the petroliferous strata. He supposes it to have been stored in its subterranean reservoirs from that time to the present.

In these several statements as to origin, two questions are seen to be especially prominent, viz.: What particular kinds or classes of rocks are the sources of petroleum, and what is the nature of the chemical processes involved in its production?

In answering the first question, we find the views of Hunt and Newberry distinctly opposed to each other. Hunt counts limestones the principal source of petroleum, and denies that it has been produced by distillation from bituminous shales, while Newberry finds in these shales the main source of both oil and gas, and vigorously opposes the view that limestones are ever an important source of either. (Geol. of Ohio, I, 159.)

It is not necessary to follow the discussion in relation to these points further. It is enough to say that in the light of present knowledge each statement is right in its particular affirmations and wrong in its general denials. Petroleum is undoubtedly indigenous to, and derived from certain limestones, as Hunt has so strongly asserted. On the other hand, Newberry's doctrine that the great supplies of the Pennsylvania field are derived from Devonian shales, is becoming more firmly established and more generally accepted every year, though it seems likely that he has laid too much stress on bituminous shales.

In other words, the theories are not exclusive of each other. Different fields have different sources. We can accept, without inconsistency, the adventitious origin of the oil in Pennsylvania sandstones, and its indigenous origin in the shales of California, or in the limestones of Canada, Kentucky or Ohio.

The double origin of petroleum from both limestones and shalesand it is not necessary to exclude sandstones from the list of possible sources-deserves to be universally accepted. In confirmation of this double origin, it is coming to be recognized that the oil and gas derived from these two sources generally differ from each other in noticeable. respects. The oil and gas derived from limestones contain larger proportions of sulphur and nitrogen than are found in the oil and gas of the shales. Nitrogen renders the oils unstable, and sulphur compounds impart to them a rank and persistent odor, from which they can be freed only with great difficulty. In the case of the oil-bearing shales of California, the petroleum is evidently derived from the animal remains with which the formation was originally filled. In composition this oil agrees with the limestone oils already described. It contains more than four times as much nitrogen as the Mecca oil of northeastern Ohio, and its percentage of sulphur is very high. Peckham says of these California oils:

"The exceedingly unstable character of these petroleums considered in connection with the amount of nitrogen that they contain, and the vast accumulation of animal remains in the strata from which they issue, together with the fact that the fresh oils soon become filled with the larvae of insects to such an extent that pools of petroleum become pools of maggots, all lend support to the theory that the oils are of animal origin." (Vol. X, p. 69).

He speaks again of this class of petroleums as formed of animal matter that has not been subjected to destructive distillation. (Ibid. p. 71).

It now appears as if oil and gas derived from animal remains can be distinguished from those of the bituminous shales by the characters above described. Certain it is that the "limestone oils" differ in physical characteristics from the Pennsylvania oils, for example, in a marked degree. They are dark in color; they are heavy oils, their gravity ranging generally from 34° to 36° Beaume, though sometimes rising to 40° or even 42°; they have a rank odor, arising from the sulphurous compounds which they contain. The oils of Canada, Kentucky, and Tennessee, and of the new field in northwestern Ohio, all agree in these respects, and the oil and gas of the Utica shale and Hudson River group of the state fall into the same category.

The organic matter of the bituminous shales has not been positively referred in the preceding statements to a vegetable source. Such a source is highly probable, but it cannot be said to be fully demonstrated until the origin of the so-called sporangites of the shales is finally determined. There are a few geologists who are inclined to refer these forms to hydroid zoophytes (animal) rather than with Dawson to marine

rhizocarps (vegetable). Whatever their origin, they give rise to petroleum and oil of a definite character, which is in marked contrast to that of the limestone oils.

Which of these theories, as to the mode and time of origin of petroleum, has the most to commend it?

d. Discussion of Peckham's Distillation Theory.

The statement under the second head, which refers it to destructive distillation of carbonaceous matter in the rocks, by the heat involved in the elevation of the Apalachian Mountain system, is the latest, and may well enough command our first attention.

This theory demands the agency of unusual temperature, and directs us to seek the source of heat action far below the unaltered rocks in which the petroleum is now found."

How far below? If we descend 1,000 or 1,500 feet below the Berea grit, which is the great repository of oil and gas in eastern Ohio, we reach the bottom (on an average) of the Ohio shale, and this is the only source that we know in our series of oil and gas of the Pennsylvania type. But the drill has repeatedly gone down 1,000 or 1,500 feet below the Berea grit, and not a trace or hint of metamorphic action is found in the drillings that are brought up. In such drillings from the deep well at Canal Dover, 2,700 feet below the surface, and even 1,800 feet below the Berea grit, the microscopic spores that make so characteristic a feature of the black shales were found in normal condition. vations attest not only the general uniformity of the shale formation throughout the state and at all depths, but also the entire absence of any appearance of metamorphic action.

All obser

The same line of facts obtains in regard to the limestones underneath the shales. They have been penetrated to a great depth. The drill in the well of the Cleveland rolling-mill rested at 3,200 feet below the surface, but the limestones at the bottom of the hole showed no signs whatever of metamorphism. The same is true of all the deep borings of northwestern Ohio. Nearly the whole of the Lower Silurian system has been penetrated there, and new supplies of oil and gas are found in these rocks, but they obviously come from the limestone themselves, and differ in a marked degree from the oil and gas of the shales. In Canada the Trenton limestone bears oil where it is separated by only a stratum of sandstone from the old granite floor of the continent.

But in the second place, Peckham demands for oil-production "slow and gentle changes at low temperature." We must again ask for a

limit. How low a temperature? Must it not be high enough to agree with the facts of observation and experiment as to the production of gas and oil by the destructive distillation of bituminous shales? The temperature at which such changes are effected in the laboratory will scarcely be placed below 400° Fahr. But the shales could not be brought to this degree withont suffering metamorphic change. They contain alkaline solutions in greater or less amount, and both Bischof and Hunt have shown that when such compounds are present, they become powerful solvents of silica and silicates at as low a temperature as 212° Fahr. If. then, the temperature had been raised to even 212° Fahr., there would have been unmistakable evidences of the fact left in the constitution of the rocks.

But if a lower temperature is proposed than that which we are obliged to use in effecting destructive distillation in the laboratory, we are compelled to ask, on what authority? It is of no use to answer that we do not know at how low temperatures this distillation can be accomplished in nature. This is true, but it is none the less true that if we reason upon the subject at all, we must be governed by the facts that our experience affords. Any other way of reaching an answer is assumption, pure and simple.

In the third place, this theory would seem to necessitate a coke or carbonized residue in the rocks which give rise to the petroleum. Inability to point out such a residue seems to have been one of the reasons that led our author to locate the source of the oil-distilling heat at such great depth. He counts a carbon residue a necessity, but he buries the rock from which the petroleum is derived so deep that we cannot expect to obtain any direct knowledge of it. As has already been shown, in doing this, he drops below the only known source of oil and gas of the Pennsylvania type.

The absence of these residual products constitute a real difficulty in the way of any distillation theory.

On the whole, then, we are obliged to conclude that Peckham's theory does not harmonize with the facts of Ohio geology, and that it cannot be used to explain the origin of the substances whose history we are seeking to trace.

e. Discussion of Newberry's Distillation Theory.

The remaining exposition of the distillation theory has already been commented upon to some extent, on a previous page. As was there shown, its scope and meaning are not entirely clear. involves destructive distillation, as it seems to, the facts and arguments