TRANSACTIONS OF SECTION C. 641 



from the combinatiim of sulphuretted hydrogeu and sulphurous acid (H*S + SO' 

 = H-0^ + 2S). Thus 



2S) 



Ca-CO' 1 ;' Ca-SOMI'O (gypsum) 



aud 



Ca^CO' 1 

 H'-'S I yield \ and 



2H=0 I [ CHS marsh ffcis 



2Ca=C0' 1 f 2Ca^S0'.H-0 (gypsum) 



2H'-S I yield l and 



2H=0-' J 1 C-R\ or ethylene. 



Four tables are given at the end of the paper, showing the formulae for the 

 homologuesof ethylene and marsh gas resulting from the increase in regular grada- 

 tion of the same constituents. 



It is explained that these effects must have occurred, not at periods of acute 

 volcanic eruptions, but in- conditions which may be and have been observed at the 

 j)resent time wherever there are active solfataras, or furaaroles, at work. Descrip- 

 tions of the action of solfataras by the late Sir Richard Burton and a British 

 Consul in 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 bitu- 

 men, with the same activity for the last fifteen centuries.' Probably at all these 

 .salfataras, 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 uuder great pressure from a great deptli. 



III. and IV. — Besides the space occupied by '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 equal 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 hydrocarbon vapours 

 were absorbed hito and condensed in contiguous clays and shales, and perhaps 

 also in beds of coal, only partially consolidated at the time. There is an extensive 

 hituminous 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 ' Encyclopedia 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 compo- 

 sition of paraffin oils, in accordance with ordinary operations of Nature during 

 successive geological periods. 



4. A Comparison hetween the Blocks of South Pembrolieshire and those of 

 North Devon. By Henry Hicks, M.B., F.B.S., Sec. Oeol. Soc. 



The clear succession from the Silurian rocks to the Carboniferous to be observed 

 in many sections in South Pembrokeshire offers, in the author's opinion, the key to 

 the true interpretation of the succession in the rocks of North Devon, for there 

 1891. TT 



