ORIGIN AND DURATION OF PETROLEUM. 273 



Since the above was written in February, 1880 I have 

 tested this luminous paint (Balmain's patent). Practically, 

 I find it unsatisfactory. In the first place, its endurance is 

 far shorter than is stated. It begins to fade almost imme- 

 diately the light is withdrawn, and in the course of an hour 

 or two it is, for all practical use -though not absolutely 

 extinguished. Besides this it emits a very unpleasant odor 

 painfully resembling sewage and sulphureted hydrogen. 

 This is doubtless due to the sulphur compound, but is, I 

 have no doubt, quite harmless in spite of its suggestions. 



THE ORIGIN AND PROBABLE DURATION OF 

 PETROLEUM. 



IN spite of the enormous quantities of mineral oil that 

 are continuously drawn from the earth, and the many places 

 from which it may thus be drawn, geologists are still puz- 

 zled to account for it. If it were commonly associated with 

 coal the problem of its origin would be solved at once. We 

 should then be satisfied that natural mineral oil is produced 

 in the same manner as the artificial product, i.e., by the 

 heating and consequent distillation of certain kinds of coal 

 or of bituminous shales ; but, as a matter of fact, -it is but 

 rarely that petroleum is found in the midst of coal seams, 

 though it is sometimes so found. 



I visited, some years ago, a coal-mine in Shropshire, 

 known as " the tarry pit," thus named on account of the 

 large quantity of crude mineral oil of a rather coarse quality 

 that exuded from the strata pierced by the shaft. It ran 

 down the sides of the shaft, filled the "sumph" (i.e., the 

 well at the bottom of the shaft in which the water draining 

 from the mine should accumulate for pumping), and an- 

 noyed the colliers so seriously that they refused to work in 

 the mine unless the nuisance were abolished. It was abol- 

 ished by " tubbing" the shaft with an oil-proof lining built 

 round that part from which the oil issued. The " tar" as 

 the crude oil was called, was then pumped out of the sumph, 



