material quantitatively recedes. If such rocks further contain many small fissures, their absorbing and yielding capacities are considerably increased. Such fissures, however, were formed by the flexures of the strata at their turning points, on the axes of the anticlinal and synclinal, while the connecting legs were least bent and broken.

When a complex of strata consisting of alternate beds of more elastic and of more brittle, less solid rocks are thrown into folds, it may a thousand times be proved in nature that the brittle rock strata, for instance limestone and conglomerate, are split asunder on the turning points of the folds, while the tougher strata, for instance shales, can follow these turnings without splitting. If, however, the bending exceeds a certain limit, whereby the duration of deformation is of essential importance, the tougher upcast strata-in Pennsylvania the schists and shales -are also broken and the oil can then ascend in the cracks extending to the surface and flow out, whereby large quantities of it are withdrawn from the conglomerate reservoir.

Hence there must exist a definite belt of anticlinals and synclinals, inside of which the flexures of the strata have been so great that on their turning points the conglomerate strata were split asunder as much as possible without fissures extending to the surface having been formed in the schists and shales; in consequence of which the absorbing and yielding capacities of the conglomerates were increased to the maximum though the oil could not escape. If the flexures were too small, i. e. if the strata were folded not at all or too little, no cracks were formed in the oil-rock, and the latter when opened by boring would yield less oil. If, on the other hand, the flexures were too large, the greater part of the oil had run out before the deposit was opened by man.

That gas occurs chiefly in the anticlinals and more seldom in the synclinals is explained by H. H. Chance' by the collection of water in the latter, they being the deeper portions of the

'The Anticlinal Theory of Natural Gas. Trans. Am. Inst. of Mining Engineers,

porous strata, and the consequent displacement of the gas; but where water is absent the synclinals may also carry gas. Mr. Chance will no doubt permit the application of his view to the distribution of oil inside of a folded complex of strata.

Let us briefly sum up these discussions. By itself the dip of a stratum whether anticlinal or synclinal cannot be declared to be oil-bearing, there being necessary also a porous rock that absorbs and yields the oil. Where such rock is bent to a certain degree it will be richest in oil. Generally speaking the anticlinals of porous rocks are richer in oil than the synclinals.

The explanations given above refer to the conditions in Pennsylvania and adjoining districts. That elsewhere the structure of the strata may also be of essential importance, is shown by the investigations of the occurrence of petroleum in the Carpathian mountains by C. M. Paul and E. Tietze.' They arrive at the final conclusion that "one thing seems to be certain in the latter respect (in regard to special kinds of complication in the position of strata or disturbance) that the prospects of striking oil by boring are better on the elevation of strata-saddles than in the depth of strata-basins, the conditions prevailing, among others, at Boryslaw, Bóbrka, Mrasznica, Orów and Ropianka, being at least favorable to this view."

The conclusions of these investigators are confirmed by a fact in the Galician territory. At Pokar near Skole, Galicia, the oil occurs in the menilite slate, which dips 40° to 50° S W and in separate strata is rich in fish remains, and in higher strata in imbedded hornstone or chert. The productive shafts are throughout put down to the above-mentioned slate, but only those gave satisfactory results and have been productive for several years which are located in a secondary anticlinal which runs towards S W, hence crossways to the principal bearing of the strata and in this direction also dips down. The principal saddle of melinite slate is destroyed, this occurring frequently in the Carpathian mountains.

Special attention may here be called to such small lateral 1 Jahrb. Geol. Reichs-Anst., 1879, 302.

saddles, which are placed more or less crossways to the principal bearing of the strata and which are plainly perceptible only in detailed maps.

The facts previously mentioned confirm an actual concentration of oil along the anticlinal ridges; related to this, but not identical with it, is the phenomenon recurring in many regions that the natural oil-springs issue forth along the anticlinals, which, however, does not prove an actual concentration of oil in the latter, because the outflow of oil may be due to the fact that the anticlinal fissures extend to the surface, while the synclinal may be closed on top, thus preventing the oil from reaching the surface.

A few cases of this kind may here be mentioned.

In Ohio and West Virginia the oil issues from fissures corresponding to the anticlinal axes. The occurrence of oil in Kentucky and Tennessee corresponds to the anticlinal parallel to the Alleghanies, which divides the carboniferous formation into two coal fields.

As regards the North German occurrence of oil, Bunsen,' as far back as 1839, has shown that the most important localities of oil and maltha lie in a nearly straight line, which running from southeast to northwest connects the localities, Wietze, Haenigsen and Oedesse.

The Carpathian mountains in the Bukowina, which form the continuation of those in Galicia, have been investigated by Bruno Walter. He showed that all natural oil springs in that country belong to the lower chalk strata, especially to the Ropianka strata, and lie in three lines parallel to the Carpathian mountains, which correspond to anticlinals.

The favorable influence of the anticlinals as regard the Roumanian oil regions has been shown by Paul and Olezewski.

The favorable influence of the saddles of the folds upon the oil-bearing strata of Apscheron (neighborhood of Baku) is also well known, and we will here quote H. Abich's' remarks re

13. Jahresber. Verein f. Naturkunde in Cassel, S. 12. "Jahrb. geol. ReichsAnst., 1879.

garding this region: Wherever at Apscheron naphtha in a fluid or inspissated form spontaneously issues forth immediately from the old tertiary formation, and the presence of larger accumulations of bitumen at a greater depth is, according to experience, probable, the stratification is in the form of an elliptical, mostly flat arch, which is either closed or anticlinally opened in the direction of its longitudinal axis."

On the northern declivity of the Caucasus the anticlinals also exert an extremely favorable influence. From a Russian official document' we quote as follows: "With the distance from the mouth of the Kuban the effects of the upheaving forces become more and more apparent. Oil springs appear on the elevated points in the anticlinal dips, as well as mud volcanoes, bitter springs and sulphur springs. This relation between oil springs and mud volcanoes is so constant that the latter may be used in searching for the former. The springs on the elevated lines yield a far more fluid product than those of the monoclinal dips. The general distribution of the springs in this region is closely connected with the direction of the upheaval of the sedimentary strata."

In regard to the trans-Caspian oil region Dr. Hj. Sjögren has recently shown that both of the larger oil localities—Neftjanaja gora and Buja-Dagh (with up to 130° F. hot brine springs)— visited by him, lie upon the ridges of two anticlinals, the structure of one of which is symmetrical and of the other unsymmetrical.

According to Zincken, petroleum occurs about 29 miles SS W of Chokand, Russian Turkestan, on the anticlinal axis of upheaved chalk strata. At Khatan, Bellouchistan, oil occurs, according to R. Townsend on the summit of an anticlinal, as can be readily recognized from the profile of this region given by him.

H. B. Medlicott' repeatedly refers to the fact that not only in Ministere du Domains de l'état, 1879. Jahrb. geol. * Report on the Petr. Expl. at Khatan; Rec. Geol. Surv. 3 Note on the occurrence of Petroleum in India; Rec. Geol.

Apercu des Mines du Reichs-Anst., 1887, S. 47. of India, 1886, 19, 204. Surv. of India, 1886.