248 THE JOURNAL OF GEOLOGY. 



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 arena- 

 ceous rocks, while in the Lower Carboniferous deposits in other 

 parts of Scotland no oil shales of any value have been yet dis- 

 covered. 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 accumu- 

 lated 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 Pent- 

 land 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 amonsf the Califerious sandstones of the 



