case, we had to deal with a primary accumulation resembling a deposit.

The above mentioned deposits as well as those previously described are only secondary. They are found, as well as both kinds combined, in several localities, for instance, in Canada.

Regarding the question of the formation of petroleum these secondary deposits are, however, of as little importance as oil reservoirs above ground; they suggest only a seat of origin. Those investigators who locate the seat of origin in the red-hot depths of the earth moreover deny the presence of a primary deposit, since according to that opinion no accumulation can take place in the retort-in the seat of origin—but only in the cooled receiver, namely in the fissures leading to the surface and the porous rock strata connected with them.

Hence, independent of the practical importance, it is of theoretical interest to inquire whether primary oil deposits exist. This can only be decided by observation. Since the origin of petroleum, like that of coal, from organic remains has to be accepted as settled, it has first to be determined by observation whether an accumulation of petroleum corresponds to a deposit, i. c., to a concordantly imbedded layer of strata. It must further be shown that the oil (or bitumen in general) occurring therein has not been transported from the exterior, but has been formed in this deposit.

A few localities may here be mentioned in which primary petroleum deposits have been established: In the same localities secondary deposits may, of course, have been formed, as soon as the oil had a chance to escape from the original deposit.

Peckham says in regard to the petroleum of California and Tennessee that it has without doubt been formed in the shales from which it issues.

T. Sterry Hunt is of the opinion that the oil-bearing Niagara limestone, especially at Chicago, Illinois, is a primary deposit. To the same author we are indebted for a very interesting observation in the township of Bertie, which is on the Niagara River opposite Buffalo. He says: "Here in a quarry are seen

massive beds, slightly inclined, composed of a solid, crystalline encrinal limestone, which appears not only destitute of petroleum, but, from the water by which it is impregnated, to be impermeable to it. In some of the beds are large corals of genus Heliophyllum, the pores of which are open but contain no oil. Two beds, however, one of 3 and one of 8 inches, which are interstratified with these, are in a great part made up of species of Heliophyllum and Favosites, the cells of which are full of petroleum. The layer of 3 inches was seen to be twice interrupted in an exposure of a few feet, thus presenting lenticular beds of the oil-bearing rocks." These facts prove without doubt that the petroleum occurs here in primary deposit, since the presence of a fissure along which the oil could have been transported, could not be established.

Hunt arrives at the same result in regard to the limestones carrying corals and oil of Canada. He says: "The absence of oil from the unfilled cells of corals in the adjacent and interstratified beds forbids the idea of its introduction into these strata either by distillation or infiltration." The same observations apply to the Trenton limestone of which he gives examples in Ontario.

The occurrence of oil in Kentucky, which appears in a conglomerate and sandstone filled. with broken and already macerated vegetable remains (?) on the base of the coal formation is, according to J. P. Lesley, also in primary deposit.

According to E. Orton the oil in northwestern Ohio is also deposited in its original seat of formation.

The asphalt of Trinidad is, according to G. P. Wall, in situ in certain strata of the upper Newer Parian group.

Bright and Prestwich consider the petroleum of England as formed in the limestones and shales. Concerning the origin of the petroleum of Shropshire, Arthur Aiken says: "The thirtyfirst and thirty-second strata are coarse-grained sandstone entirely penetrated by petroleum, are, both together, 151⁄2 feet thick, and have a sandy bed of shale-clay about 4 feet thick interposed between them. By certain geologists this reservoir

of petroleum has been supposed to be sublimed from beds of coal that lie below, a hypothesis not easily reconciled to present appearances, especially as it omits to explain how petroleum in the upper of these beds could have passed through the interposed bed of clay so entirely as to leave no trace behind. It is also worthy of remark that the nearest coal is only 6 inches thick, and is separated from the above beds by a mass 96 feet in thickness, consisting of sandstone and clay strata without any mixture of petroleum." Moreover, these facts do not allow of the assumption that the oil has been forced upwards either in the form of gas or in liquid drops. There is but one explanation, and that is, the oil is in primary deposit.

A. Andreæ, by reason of his thorough study of the occur rence of petroleum in tertiary strata, arrives at the conclusion. that the oil of Upper as well as Lower Alsace is in primary deposit. The brackish water petrifactions, as well as the other geological conditions, point towards the accumulation of the organic material in a lagoon or a delta; the transformation of the organisms into petroleum has been effected under the exclusion of air and great pressure.

Concerning the occurrence of bitumen at Seyssel on the Rhone, France, D. C. Davies says: "The chalk formation contains three beds of bituminous chalk 10 to 13 feet thick, and have interposed between them deposits of white chalk not impregnated with bitumen, 3 to 50 feet thick. The impregnated beds are in some places highly crystalline and consist in others of the remains of shells accompanied by some fish teeth. The bitumen occurs in geodes, cavities, and in beds, and forms 8 to 10 per cent. of the entire mass."

Now, since some limestone beds are bituminous, and others free from bitumen, and the occurrence of a fissure for the conveyance of the bitumen has not been observed, the oily substance can, in this case, be only in primary deposit.

Regarding the occurrence of mineral tar at Limmer, Hanover, H. Credner is of the opinion that it is of animal origin as well as in the original deposit. Regarding the North German finds,

Eck says: "We have every reason to believe the mineral tar occurring in the clays of the lias and of the brown Jura, and in the rocks of the Wealden formation, to belong originally to these strata."

In the Carpathian zone an oil level belongs to the fish-shale, which, as indicated by its name, carries remains of fishes. Below and above it is sandstone which contains no oil, notwithstanding it is a porous rock, while the fish-shale is difficult to penetrate by fluids. In this case the introduction of petroleum from the exterior is, therefore, entirely excluded, and it must have been formed in the shale bed. The fact of the frequent occurrence of fish remains in this shale and the entire absence of vegetable remains furnishes another proof of the animal origin of petroleum.

In Galicia it may also be frequently observed that in a fishshale group the oil is preponderantly fixed in one or more beds. There may be two causes for this phenomenon, which have to be determined for each particular case; such interstratified oil beds correspond either to a special concentration of fish remains, or to the interstratification of a porous rock, for instance, sandstone.

H. B. Medlicott' refers to the fact that all occurrences of petroleum in the Punjab belong to the eocene and only to one geological horizon in this group of strata, and he, therefore, recognizes it as a primary deposit. The occurrences of petroleum in Khatan (Belloochistan) show, according to R. Townsand," the same genetic character.

The occurrence of oil, gas and bituminous shales (pyroschists according to T. S. Hunt), by the distillation of which considerable quantities of oil may be obtained, also proves the formation of bitumen in a primary deposit, because these shales are not readily permeated by fluids and have above and below them more permeable and more porous rocks, such as sandstone, limestone or dolomite, which would have more readily

201.

Note on the Occurrence of Petroleum in India (Record Geol. Surv. of India) 19, 2 Rep. Petr. Expl. at Khatan, Record of Geol. Surv. of India, 19, 204.

absorbed the oil. If some bitumen is found in the more porous rocks-generally in fissures-it is mostly in such close vicinity to the shales that it can be traced to them.

The bituminous shale can be concordantly interstratified in a shale free from bitumen, and in this case also the bitumen can be only in primary deposit.

The oil shales contain either animal remains only or besides them also vegetable remains. That the latter is only of passive importance in the formation of bitumen has previously been mentioned.

Of shales especially rich in oil may only be mentioned: Those of the Lothians in the British coal formation, with ostracodes, fishes, coprolites, etc.; the shales of the upper lias of Suabia and Franconia, which are extraordinarily rich in animal remains, among them the well-known saurians, fishes, and cuttle fishes (ink-bag and frame of loligo); the oil slate 78 to 98 feet thick, which at Steierdorf is concordantly interstratified in a tract of shale overlying the upper vein.

The bitumen of the Ohio shale, which in the eastern part of Ohio attains a thickness of up to 650 feet, being uniformly distributed through the entire group of strata, can only be of primary naturc. The same applies to the Heldenberg, Clinton, Niagara, corniferous and other limestones of the Eastern portion of North America. Hunt has made a calculation showing the amount of petroleum which the oil-bearing dolomite of Chicago holds to the square mile for every foot of thickness in the stratum. "If we apply," says E. Orton, "a like calculation to the rocks of the Ohio shale, we shall find the total amount of oil enormously large. We may take, for example, the Waterlime stratum, which is notably and almost universally petroliferous. Estimating its petroleum content at one-tenth of one per cent., and the thickness of the stratum at 500 feet, both of which figures are probably within the limits, we find the petroleum contained in it more than 2,500,000 barrels to the square mile. The total production of the great oil field of Pennsylvania and New York to January, 1885, is 261,000,000 barrels. It would