II.  As evidence of volcanic action in close proximity to petroleum strata, the mud volcanoes at Baku and in Burma are described, and a sulphur mine in Spain is mentioned (with which the writer is well acquainted), situated near an extinct volcano, where a perpetual gas flame in a neighboring chapel and other symptoms indicate that petroleum is not far off.  While engaged in studying the geological conditions of this mine, the author observed that Dr. Christoff Bischoff records in his writings that he had produced sulphur in his own laboratory by passing hot volcanic gases through chalk, which, when expressed in a chemical formula, leads at once to the postulate that, in addition to sulphur, ethylene, and all its homologues (C_{n}H_{2n}), which are the oils predominating at Baku, would be produced by treating: 

2, 3, 4,  5 equivs. of carbonate of lime (limestone) with
2, 3, 4,  5   "        sulphurous acid (SO_{2}) and
4, 6, 8, 10  "         sulphureted hydrogen (H_{2}S);

and that marsh gas and its homologues, which are the oils predominating in Pennsylvania, would be produced by treating: 

1, 2, 3, 4, 5 equivs. of carbonate of lime with
1, 2, 3, 4, 5   "        sulphurous acid and
3, 5, 7, 9, 11  "        sulphureted hydrogen.

Thus we find that: 

Carbonate of lime, 2CaCO_{3}, } { 2(CaSO.H_{2}O) (gypsum),
Sulphurous acid, 2SO_{2}, and } yield { 4S (sulphur), and
Sulphureted hydrogen, 4H_{2}S, } { C_{2}H_{4}, which is

          
                                                                        { ethylene.

And that: 

Carbonate of lime, CaCO_{3}    }         { (CaSO_{4}.H_{2}O) (gypsum),
Sulphurous acid, SO_{2}, and   }  yield  { 3S (sulphur) and
Sulphureted hydrogen, 3H_{2}S, }         { CH4, which is marsh gas.

So that these and all their homologues, in fact petroleum in all its varieties, would be produced in nature by the action of volcanic gases on limestone.

But much the most abundant of the volcanic gases appear at the surface as steam, and petroleum seems to have been more usually produced without sulphurous acid, and with part of the sulphureted hydrogen (H_{2}S) replaced by H_{2}O (steam) or H_{2}O_{2} (peroxide of hydrogen), which is the product that results from the combination of sulphureted hydrogen and sulphurous acid: 

    (H_{2}S + SO_{2} == H_{2}O_{2} + 2S).

It is a powerful oxidizing agent, and it converts sulphurous into sulphuric acid.  Thus: 

  CaCO_{3} } { CaSO_{4}.H_{2}O (gypsum)
  H_{2}S, } yield { and
  2H_{2}O, } { CH_{4}, which is marsh gas.

And

2CaCO_{3},    }         { 2CaSO_{4}.H_{2}O
2H_{2}S,      }  yield  { and
2H_{2}O_{2},  }         { C_{2}H_{4}, which is ethylene.

Tables are given showing the formulae for the homologues of ethylene and marsh gas resulting from the increase in regular gradation of the same constituents.