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of which are still preserved in the Science and Art Museum in Edinburgh. There can be little doubt that this "mineral" owes its origin to the distillation of the bituminous matters by the igneous intrusions in the vicinity of the overlying oil shale.

The oil shales occur within an area roughly twenty miles in diameter. On the north shore of the Firth of Forth only one seam of workable quality is known, and all the others have apparently disappeared and become replaced by more arenaceous rocks, while in the Lower Carboniferous deposits in other parts of Scotland no oil shales of any value have been yet discovered. These valuable deposits appear to have been found in broad lagoons into which vegetable matter was brought in a very fine state of division, and laid down along with a small quantity of inorganic silt under conditions of great tranquillity. That the hydrocarbon is however sometimes of animal origin is clear from the quantity of cyprids that make up some of the shales. Large plant remains are rare, but beautifully preserved fronds of sphenopteris affinis, and other ferns are abundant in some of the beds of oil shale. There cannot have been currents of any strength sweeping through the lakes of the Scottish oil-shale period, otherwise the light organic particles would have been at once swept away, and this order of things must, with periodical interruptions, have obtained within the shale region for a long succession of ages, during which deposits accumulated to a depth of over 3,000 feet.

Liquid petroleum has been occasionally found exuding in small quantities from the joints of these sedimentary rocks, and there is at St. Catherines, about three miles south of Edinburgh, a spring situated on the line of the great fault east of the Pentland axis already referred to, known for many centuries as the Balm Well, whose surface is covered by a film of mineral oil derived no doubt from the slow distillation of the oil shales on the downthrow side of the dislocation. We cannot, however, boast of anything like the famous oil wells of Pennsylvania, which I had the pleasure of visiting in 1891, and even were there rich oil sands among the Califerious sandstones of the