550 PETROLEUM 



cost 7.000/. sterling to fit up a shale- work giving the lowest yield ; and the profits 

 would bo fractional compared with those of the oil-well. This competition has driven 

 the crude-oil trade of Britain into the hands of large capitalists. But the oil-maker 

 calculates on the gross profits of a large turn-over, and on his advantage over his 

 Pennsylvanian competitor in having sulphate of ammonia, paraffin, and other ore- 

 products. The enormous quantity of used petroleum-barrels in the British market is 

 also a great source of profit. 



As regards the origin of petrolexim and analogous bituminous substances, there can 

 be but little doubt that they are derived from the decomposition of organic matter 

 in the rocks containing them. The changes forming part of the great series whereby 

 organised structures, containing carbon, oxygen, and hydrogen, become altered into 

 peat, lignite, coal, anthracite, and graphite, are too well known to be dwelt upon here 

 at length ; suffice it to say, that they consist in the abstraction of variable quantities 

 of carbonic acid, water, and marsh-gas (C 2 H 4 ). From the results of observations of 

 the Geological Survey of Canada, Dr. Sterry Hunt, Mr. Wall, and others, it would 

 appear that the separation of these hydrocarbons is the first stage of carbonaceous 

 metamorpliism, and that such substances when under favourable conditions that 

 is, when kept from the access of air, as in the cavities of limestones, or in sand- 

 stones or shales covered by impermeable beds may be preserved intact ; but when 

 they are allowed to come to the surface (as, for instance, in rising through cracks 

 and superficial gravels) oxidation takes place, the greater part of the hydrogen is 

 removed, and ultimately asphalt and coaly substances are produced. That much of 

 the petroleum of the older rocks may be derived from the decomposition of animal 

 matter is evident by its presence in considerable amount in the cells of coral, in 

 Corniferous limestone, which contains exclusively marine remains, and is not per- 

 meable to liquids from without. In peat and brown coal there is no difficulty in 

 supposing that the decomposition of the plants has given rise to the various paraffin- 

 like and other solid hydrocarbons which it contains. One particular class of these 

 substances namely, the resins, such as amber, retinite, &c. may have existed in 

 the tissues of the plants during their life, as they may all be paralleled with the 

 gum-resins of living conifers. Perhaps the most remarkable among these bitu- 

 mens is that called Scheercritc, found in the brown coals of Uznach in Switzerland, 

 and Eger in Bohemia ; which, while resembling Hatchettine, has the composition 

 of marsh-gas, showing the same relation to it that paraffin does to olefiant gas. 



Another fact in support of the animal origin of some bitumens is that furnished by 

 the bituminous odour evolved by nearly all very fossiliferous limestones, as, for in- 

 stance, the Upper Silurian and Carboniferous limestones of England, which certainly 

 contain no land-plants. 



Another view, put forward by Dr. Senft, may be of use in explaining why in certain 

 cases coals are produced and in others bituminous shales : it is, that the carbonaceous 

 substance produced in peat-bogs has the power of absorbing and fixing carburetted 

 and sulphuretted hydrogen. Now, supposing in a sea-bed the amount of decomposing 

 organic matter, marine plants, molluscs, corals, &c., to be small as compared with the 

 accompanying mineral matter (carbonate of lime, silica, clay, &c.), the hydrocarbons 

 formed would be liable to escape, and remain isolated as petroleum. But, on the 

 other hand, in the case of a great forest-growth or peat-bog decomposing under water, 

 the hydrocarbons separated would bo liable to be reabsorbed by the great excess of 

 residual carbon present, and to bo condensed, giving rise to bituminous coals. See 

 NAPHTHA; PARAFFIN. 



Petroleum Imports in 1873. 



Tuns Va j. 



Unrefined, from the United States of America . 895 12,836 



Gallons 



Refined, from the United States of America . 16,377,252 974,755 



other countries .... 58,548 5,250 



Total . . . 16,435,800 979,005 



Imports in 1874. 

 85,630 tuns; value 1,002,541. 



(For further information on this subject, consult Sterry Hunt's paper in 'American 

 Journal of Science,' vol. xxxv. p. 158 ; Senft, ulcr Humus, Torf, &c. ; Gesner on 

 ' Coal Oils ' ; and Rammelsbcrg, Mineral- Ckcmie.) 



At the old rates of wages and coals, the crude oil yielded a moderate trade-profit in 

 competition with petroleum ; but this summer (1873) many British companies have 

 considerably reduced their dividends. And the stability of our home trade will 



