bitumen and tars, or the products of the reaction of hydrogen upon the matters already condensed, that is to say, hydrocarbons more hydrogenated. For example, the hydrogen reacting upon the acetylene produces ethylene and hydride of ethylene. A new reaction of the hydrogen either upon the polymerides of the acetylene, or upon those of the ethylene, would give rise to saturated hydrocarbons such as constitute American petroleum. An almost unlimited diversity in the reaction is here possible according to the temperature and the bodies present. We can thus conceive the production by a purely mineral method of all the natural hydrocarbons by the intervention of heat, water, and alkali metals. Lastly, the tendency of the hydrocarbons to unite together so as to form more condensed matter, suffices to account for the formation of these curious compounds. This formation can also be effected in a continuous manner, since the reactions which produce it are incessantly renewed."

This beautiful and ingenious theory has more in it to commend itself to the chemist than to the geologist. The latter would find the conditions required by M. Berthelot to be absolutely wanting in the strata in which petroleum is found. The alkali metals or their carbonates are not present in or anywhere near the oil-sands. As metals they would exist as primitive material, and we must go far below these to find the conditions necessary for the formation of petroleum according to this theory. A's at present advised, therefore, we must rest our case in looking upon this product as having either an animal or vegetable

origin, or both combined. That there are difficulties attendant upon any theory we must admit, but these are being laid aside one by one as new light dawns upon us.

While, therefore, geologists are generally consenting to the opinion that petroleum is the product of a slow destructive distillation of organic remains, the point of interest, and perhaps we may say, the point of divergence in sentiment is the unsolved question whether the strata in which the oil is now found are to be regarded as the parent rocks, or whether (as for instance the oil-bearing sand-rocks) they are to be considered as the reservoirs into which the distilled product has found a permanent lodge

ment.

Both of these views have their distinguished advocates, and it cannot be denied that an array of facts may be cited to prove or disprove either one or the other of these controverted positions. In the end it will probably be found to be the case, that certain gcological strata in which oil is found already formed, really form its starting point and resting place, and that certain other strata are simply receptacles for oil formed in other beds.

Upon an examination of the fragments of the oil-bearing sand-rock brought to the surface during the operation of drilling, we are unable to detect in them anything which points to such a process of destructive distillation as we have described. There is no débris, no residuary product. Could it be possible-is it within the bounds of sound inductive reasoning-that such vast quantities of organic matter as would be necessary to form a supply of oil

such as is found in these rocks, could have so wholly disappeared as to leave no vestige of their existence?

Again, it might be asked, if these sand strata were the original places of deposit for this organic matter, at what period of their formation was this material thrown there? If placed upon the ocean beach before its subsidence below the water level, the essential conditions for destructive distillation, and the formation of these hydrocarbons are wanting. There would be, it is true, an evaporation of the watery constituents of their structure, and a residuary product of their mineral elements, but under no circumstances such as we are now considering could there have been formed a single trace of oil. It is equally fallacious to conjecture the elimination of oil from such a bed of material, which had been recently placed by its subsidence below the ocean; here, again, the conditions necessary for the formation of oil are wanting; but, granting the possi bility, what would be the destination of oil so formed? Certainly it would not be to remain in the position where it was generated.

It would undoubtedly obey the laws of gravity, and, being specifically lighter than water surrounding it, it would rise to the surface and be either wafted to some place of deposit, or be dissipated by evaporation and disappear altogether.

In order to meet the conditions necessary for the formation of oil, we must therefore allow of the subsidence of this deposit (protected also from dissipation and waste by a previous covering of sand) to such a depth as where the

internal fires of the earth could perform their function of the operation. Now, while admitting this possibly reasonable supposition, we are confronted with the fact that there are to be found within the same district no less than six successive deposits of similar formation, each of which in its turn would have to be lowered to the oil-making horizon. Mr. Carll places "the vertical distance between the third oil-sand (the Venango 3d) and Mahoning sandstone at 1550 feet. Therefore when the Mahoning sandstone occupied the plane of spontaneous distillation, the third oilsand must have been 1550 feet below it, and subject by reason of this additional depth to a degree of heat much greater than that of the horizon in which the oil contained in it was formed." With this theory in view, we must suppose that the lowest in the series of these formations would have to be subjected to a higher degree of heat than either of the others and for a vastly longer period of time. The effect of this lengthened exposure upon the lowest oil-bearing rock would be to drive off by the ordinary process of distillation the lighter and more volatile' hydrocarbons, and we should expect to find the heaviest variety of petroleum. On the contrary, we find just the reverse of this, and it is the uniform experience that the lightest oils are found in the lowest sandstones, while the heavi est oils are drawn from the shallowest wells; and, as we approach the surface where it is gathered from pools dug to the depth of only a few feet, it becomes viscid, semifluid, and finally a solid asphalt.

As far, then, as we are able to form an opinion upon this

subject, from the data at present at our command, we conclude that the sand-rocks of the oil region of Western Pennsylvania are merely reservoirs for the collection and reception of the oil which has been formed from bituminous shales lying beneath the sand.

The question is an important one, not only from a scientific point of view, but also in an economic light. Having located the stratum according to a correct theory, very large amounts, now uselessly wasted in drilling for oil, might be saved.

The Sand Strata as Reservoirs.

Upon the assumption that the sand-rocks are not the parent rocks in which the petroleum was originally formed, but are merely receptacles for its reception after its formation, an interesting question is that which relates to the capacity of these strata for holding such immense volumes of oil as have already been removed and as they appear still to contain. It was doubted by many that they were the reservoirs, because it appeared impossible that a sandstone apparently so homogeneous in its structure could hold such vast quantities of oil. These assumed the necessity of large subterranean fissures or cavities. That fissures are occasionally met with in drilling wells, is a well-known fact; but that they are of such dimensions as to fulfil the required indications, we have no proof whatever, and the truth is, that the facts of the case are altogether opposed to any such theory. In the early days of oil mining, to strike