TltANSACTIONS OF SECTION C. 639 



Bavaria Lower Tertiary (Flysch). 



Italj' Eocene. 



T.,^ ,, , XT \ .... Neocomian to Miocene. 



North-east Hungary ) 



Poland 1 



Boumania ^ . . . . . Miocene. 



Caucasus I 



The important districts of Baku occur on plains over anticliuals of Miocene beds. 

 The petroleum-bearing' sands are interstratified with impervious clays, separating 

 the strata into distinct productive horizons. 



In Algeria oil occurs in Lower Tertiary beds. The Egyptian petroleum comes 

 from Miocene strata. 



Petroleum seems to be unknown in peninsular India ; but it occurs in many 

 places along the flanks of the Himalayan range, and also in Lower Burma, generally 

 in Lower Tertiary strata. In Upper Burma and Japan the oil-bearing rocks are 

 probably Newer Tertiary. In all these areas the beds are greatly disturbed, and 

 the same is the case with the great Carpathian field ; but it frequently happens 

 that the most productive regions are along anticlinal lines. 



In New Zealand oil occurs in Cretaceous and Tertiary strata. 



Petroleum and gas almost universally occur associated with brine. This may 

 come wholly or partly from the decomposition of the animal matter which has 

 produced the hydrocarbons, together with the remains of the sea- water originally 

 present in the rocks. But the frequent occurrence of rock-salt in the neighbourhood 

 of petroleum-bearing districts is worthy of note. 



Summary. — The main points to be considered in respect to the geological con- 

 ditions under which petroleum and gas occur in quautitj' seem to be as follows : — 



1. They occur in rocks of all geological ages, from Silurian upwards. The 

 most productive areas are Palteozoic in North America, Miocene in the Caucasus; 



2. There is no relation to true volcanic action. 



3. The most productive areas for oil in great quantity are where the strata are 

 comparatively undisturbed. Oil, but in less abundance, frequently occurs when 

 the strata are highly disturbed and contorted, but gas is rarely so found. 



4. The main requisites for a productive oil- or gas-field are a porous reservoir 

 (sandstone or limestone) and an impervious cover. 



5. Both in comparatively undisturbed and in highly disturbed areas, an anti- 

 clinal structure often favours the accumulation of oil and gas in the domes of the 

 arches. 



6. Brine is an almost universal accompaniment of oil and gas. 



3. The Origin of Petroleum} By 0. C. D. Eoss. 



In the coui'se of introductory remarks the author contends that, owing to the 

 mystery surrounding the origin of petroleum, and to the paucity of indications 

 ■where to seek for it, practical men in this countrj^ distrust the permanence of the 

 supply, and hesitate to adopt it for many useful purposes ; while the object of 

 this paper is to suggest a way of resolving the mystery which is calculated to 

 dissipate that distrust. The theories suggested by Reichenbach, Berthelot, Men- 

 delejeff, Virlet, Verneuil, Peckham, and others, which are briefly described, make 

 no attempt to account for the remarkable variety in its chemical composition, in its 

 specific gravity, its boiling points, &c., and are all founded on some hypothetical 

 process which differs from any with which we are acquainted; but modern geo- 

 logists are agreed that (as a rule) the records of the earth's history should be read 

 in accordance with those laws of Nature which contimie in force at the present 

 day. E.g., the decomposition of fish would not now produce paraffin oil ; hence 

 we can hardly believe it possible thousands, or millions, of jears ago, so long as 

 it can be shown that any of the ordinary processes of Nature is calculated to 

 produce it. The chief characteristics of petroleum strata are enumerated as : I. The 



• See the Chemical News for October IG, 1891. 



