quantity, since in such cases the disturbance of the stratification has been so profound that all the natural gas generated in the past would long ago have escaped into the air through fissures that traverse all the beds. Another limitation might be added, which would confine the area where great gas flows may be obtained, to those underlaid by a considerable thickness of bituminous shale."

Where the terrace structure prevails, as is particularly the case in North-Western Ohio and Central Indiana, the oil and gas are naturally found over large areas, though a slight local elevation usually gives rise to a considerable accumulation, as is notably exemplified in the case of some of the wells at Lima, where the general dip of the strata is practically negligible.

In the districts traversed by anticlines, however, the yielding portions of the strata are mainly confined to the anticlines, the gas accumulating on the summit of the curves. In Western Pennsylvania these gas areas are seldom more than a mile or two wide and a few miles in length. Mr. Ashburner, in a paper read before the American Institute of Mining Engineers in September, 1885, on the "Geology of Natural Gas in Pennsylvania and New York," has pointed out that though many of the largest gas wells have been found along anticlinal axes, the exceptions, including many wells which have produced gas along the synclines, are numerous and important.

As regards the Eastern hemisphere, the anticlinal theory is also found to apply, evidence having particularly been collected in the case of the Caucasian and Carpathian fields, and of those of India. Professor Abich has shown that it applies to the Apsheron peninsula; and Sjögren2 believes that the oil-producing districts visited by him at Neftjanaga and Buda-Dagh, in the Transcaspian region, both lie on anticlinals. Zincken has found that Khokand, in Russian Turkestan, yields its oil along anticlinal axes. The Carpathian deposits have also been shown to possess an anticlinal structure, in so far that oil is found at the tops of the curved strata, as at Boryslaw, Bobrka, and Ropienka, rather than at the lower parts. BrunoWalter has shown the application of the theory to the deposits of Bukowina; and Paul and Olszewski have found it to apply to those of Roumania. Its application to the deposits of Khátan has been shown by Townsend, and of the Punjab by Zincken.5 Mr. Lyman remarks that it applies to many of the oil wells of Japan.

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The earlier searchers for petroleum in America soon became aware of many of the principal factors which govern its occurrence, the three oil sands noticed by the drillers in Venango County being among the earliest observed features of the Pennsylvanian field, as was also the tendency of the productive wells to follow clearly-defined lines and

1 Jahr. der Geol. Reichs-Anstalt, 1879.

2 Loc. cit., 1887, 47.

3 Paul and Tietze, Jahr. der Geol. Reichs-Anstalt, 1879, 302.

4 Rep. on the Petroleum Exploration at Khútan, Geol. Survey of India, 1886, xix. 204.

5 Geol. Horiz. Fossil Kohlen, &c., 114.

Geol. Survey of the Oil Lands of Japan, Tokio, 1877 and 1878.

map out an "oil belt," within which the probability of a response to the drill far exceeded that of the outlying territory.

Mr. Carll1 has pointed out that "the several groups of oil-producing rocks are locally well defined under certain areas; but they have their geographical as well as their geological limits, and, as far as at present known, the geographical limit of one group never overlaps that of another." Speaking of the Pennsylvanian fields, he continues "If we take a map and outline upon it the limits of the Smith's Ferry and Slippery Rock oil-producing district, and then the Butler, Clarion, and Venango, and then the Warren, and then the Bradford, we shall see that each has its own particular locus, and that the different districts are separated from one another by areas of greater or less extent, which have been pretty thoroughly tested by the drill and proven to be unproductive."

The Oil Belt. The "oil belt" theory appears to have been originated as early as 1867 by Mr. C. D. Angell, a very successful operator, who followed it up with such success that it led to the opening up by others of districts which might otherwise have long remained unexplored. The theory assumed that the oil always runs along lines of definite direction, and led to many wells being drilled along certain degree lines. Although the theory is now practically abandoned, most of the productive wells within individual oil pools have been located along definite degree lines, as pointed out by Mr. Ashburner.

Most of the oil-producing areas of Pennsylvania and Western Virginia are included in a comparatively narrow belt of country stretching from north-east to south-west. (See Fig. 1.) The belt may be followed across Ohio, but the deposits of South-Eastern Ohio are independent of it. The oil belt of Galicia has, so far as it has yet been defined, a length of about 220 miles, with a breadth of from 40 to 60 miles, and extends in a general north-westerly and southeasterly direction. In the Baku fields, the deposits extend in a north-east and south-west direction, as in Pennsylvania.

General Distribution.-On referring to the Frontispiece and Plate I., it will be seen that the principal petroleum deposits of the world occur along well-defined lines, and are intimately associated with the principal mountain chains of the world. In the New World oil is found at the north-west in Alaska and in the Mackenzie district, and other producing areas extend from Point Gaspé in Quebec to Nashville in Tennessee; from San Francisco to San Diego; from Northern Nebraska along the Missouri River, and directly south of the Gulf of Mexico; from Cuba through the Leeward and Windward Islands to Trinidad, and thence along the northern portions of South America to the Magdalena River, and southward to Cape Blanco in Peru (Peckham).

The gas area of North America stretches from the Hudson River in the east to the Pacific Coast in the west, and from Lake Michigan in the north to the Gulf of Mexico in the south. Experience has shown 1 Seventh Rep. on the Oil and Gas Wells of Pennsylvania, 1890, 120.

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that little or no gas occurs along the Atlantic Coast, while the valley of the Mississippi forms the chief field, especially in the Ohio limestones and in the Pennsylvanian palæozoic deposits.

In the Old World (see Plate I.), passing westward from Baku on the eastern confines of Europe, oil is found in the neighbourhood of Tiflis and between Poti and Batoum, and at many other points along the range of the Caucasus mountains; while farther westward are the oil fields of Ilsky and Koudako on the Taman peninsula, and those of Kertch in the Crimea. On the northern slopes of the Carpathians will be found the oil fields of Galicia; while on the south-eastern and southern slopes of the Southern Carpathians or Transylvanian Alps lie the important deposits of Roumania, and the less-known fields of Bukowina, Transylvania, and Hungary. An extension of this general south-easterly and northwesterly line passes through the neighbourhood of Hanover, where petroleum is also worked. A line parallel to and south of this line includes a number of localities where oil is said to occur on the Dalmatian and Albanian coasts, near the Dinaric Alps and the Pindus mountains; and to the north-west of these lies the somewhat important oil field of Alsace, bordered by the Vosges mountains.

Another north-westerly and south-easterly line lying further south, includes the oil-bearing rocks of Italy, following the general direction of the Appenines; and to the south-east lie the historical petroleum springs of Zante. The oil deposits of Sicily lie on a further parallel line, whose north-westerly prolongation would pass but little north of the Pyrenees, where petroleum is also found. A line drawn parallel to these, and passing in a south-easterly direction near the southern part of Spain (where oil has been met with), not far from the range of the Sierra Nevada mountains, will traverse the Algerian deposits in the neighbourhood of Oran, with the Atlas mountains not far inland.

NORTH AMERICA.

In the United States, at the close of 1893, the six principal oilproducing States were as follows, in the order of production :— Pennsylvania, Ohio, Western Virginia, New York, Indiana, and Colorado (see Plate II.) Some production, with considerable promise for the future, occurs in other states, as mentioned hereafter, and in Canada there are, in addition to the proved oil lands, large areas of untested territory. In the fields of Pennsylvania, New York, and Western Virginia, the yielding strata belong to the Carboniferous and Devonian periods, and the most productive include the Mahoning sandstone and the Bradford "third oil sand" immediately overlying the Devonian slates and shales. Every well-defined and persistent sandstone, however, discovered below the Pottsville conglomerate, has produced oil or gas in paying quantity.

The principal oil-horizon of Canada is confined to the Corniferous limestone, still older than the Devonian slates and shales, while in