508 Notices of Memoirs — W. Topley — On Petroleum. 



Iceland are quoted, also a paragraph from Lyell's "Principles of 

 Geology," in which he says that the mud-volcanoes at Girgenti, in 

 the Tertiary limestone formation, " are known to have been casting 

 out water, mixed with mud and bitumen, with the same activity for 

 the last fifteen centuries." Probably at all these solfataras, if the 

 gases traverse limestone, fresh deposits of oil-bearing strata are 

 accumulating; and how much may there not have been produced 

 during fifteen centuries ! 



Gypsum may also be an indication of oil-bearing strata, for the 

 substitution in limestone of sulphuric for carbonic acid can only 

 be accounted for by the action of these sulphurous gases. The 

 abundance of gypsum in the United Kingdom indicates that large 

 volumes of petroleum are probably stored in places where it has 

 never yet been sought for. Gypsum is found extensively in the 

 petroleum districts of the United States, and it underlies the rock- 

 salt beds of Middlesboro' (N.E. Yorkshire), where, on being pierced, 

 it has given passage to oil-gas, which issues abundantly mixed with 

 brine, and under great pressure from a great depth. 



III. and IV. — Besides the space occupied hy 'natural gas,' 17,000 

 million gallons of petroleum have been raised in America since 

 1860, and that quantity must have occupied 100,000,000 cubic yards ; 

 a space equel to a subterranean cavern 100 yards wide by twenty 

 feet high and eighty-two miles in length, and it is suggested that 

 beds of 'porous sandstone' could hardly find room for so much; 

 while vast receptacles may exist, carved by water out of former beds 

 of rock-salt adjoining the limestone. 



This would account for the brine ; and the increase to the molecular 

 volume of the gases consequent thereon, would in part account for 

 the pressure. It is further suggested that when no such open spaces 

 were available, the hydro-carbon vapours were absorbed into and 

 condensed in contiguous clays and shales, and perhaps also in beds 

 of coal, only partially consolidated at the time. There is an exten- 

 sive bituminous limestone formation in Persia, containing 20 per cent, 

 of bitumen ; and the theory elaborated in the paper would account 

 for bitumen and oil having been found in Canada and Tennessee 

 imbedded in limestone, which fact Mr. Peckham (in his article on 

 Petroleum in the ' Encyclopasdia Brit.,' 9th edition) thought was a 

 corroboration of his belief that some petroleums are a "product of 

 the decomposition of animal remains." 



Above all, this theory accounts for the many varieties in the 

 chemical composition of paraffin oils, in accordance with ordinary 

 operations of Nature during successive geological periods. 



X. — The Geology of Petroleum and Natural Gas. By W. 

 ToPLET, F.R.S., Assoc. Inst. C.E. 



THE object of this paper is to give a summary of some of the more 

 important facts as to the geological conditions under which 

 petroleum and natural gas are found in various parts of the world, 

 noting the geological ages of the rocks in which they occur, and the 

 influence of geological structure in determining this occurrence. 



