PETEOLEUM IIST ONTAEIO. 103 



first mentioned to the writer by the late Sir "W. E. Logan in the autumn of 1860. He was 

 then in the habit of comparing the filling of a soda-water bottle with gas and water to 

 the process which he believed went on under the impervious strata of an anticlinal. But 

 this idea seems to have originated with his colleague, Dr. T. Sterry Hunt, who mentioned 

 it in a lecture delivered in Montreal and published in the Gazette of that city on March 1st, 

 1861. According to this hypothesis, gas and oil, following hydrostatic laws, accumulate 

 at the highest points, or the domes, along anticlinal folds. All the transverse joints and 

 fissures, and the spaces or channels between beds in deep-seated, unaltered, sedimentary 

 rocks, are believed to be filled with water. The particles of gas and oil, as they are gener- 

 ated or become liberated in bitumeniferous rocks, naturally tend to rise through these 

 waters aided, perhaps, by earth-tremors and earthquake jars and shocks, such as are com- 

 mon in Canada and the northern United States. Downward projections and irregulari- 

 ties in the forms of the water-.«paces would arrest the gas and oil till these receptacles 

 became filled to overflowing. Ultimately the lighter fluids from all points, following 

 upward the slopes of the strata, would accumulate in largest quantity under the summit 

 of the dome. The gas would take the highest place, the oil the next, while the water 

 would be forced downward to an extent which would counterbalance the elastic force 

 of the gas and the weight of the accumulated petroleum. The compressed gas would 

 force back the oil, and water alike from all the upper spaces. If the crown of such an 

 anticlinal dome were tapped by a bore-hole from above, the gas would, of course, escape 

 first, followed by the oil, and then by the water This is what actually takes place in 

 productive oil regions, and experience in Canada, the United States, G-alicia, Baku, Burma, 

 etc., has shewn that the accumulations of petroleum are connected with anticlinals in the 

 manner just described. The more extensive the anticlinal, as to either breadth or depth, 

 the greater are the quantities of gas and oil which become collected, as the result of what 

 may be called the larger drainage area. Profitable supplies of petroleiim and gas are, 

 therefore, not to be looked for on anticlinals of small extent. We know, from analyses of 

 average samples, the apijroximate amount of oil which hydrocarbons in a given weight 

 or bulk of rock are capable of yielding by artificial means, but even the most moderate of 

 these calculations shew a proportion of oil and gas, far in excess of that which has ever 

 been taken from the richest areas in productive fields; and it must be remembered, too, 

 that most of this has, no doubt, been originally derived from other areas at greater or 

 less distances from those actually drawn upon. It is evident, therefore, that only a 

 small proportion of the hydrocarbons actually present in petroleum-bearing strata ever 

 become converted into the liquid or gaseous form by natural processes. As already stated, 

 experience has proved the correctness of the anticlinal theory in regard to petroleum and 

 gas ; and this fact has become useful, not only to point out probable localities for their 

 occurrence, but also to indicate large areas in which, from the attitude of the beds, it 

 would be useless to look for them, although they may be constantly forming in the strata, 

 the unfavorable indications for their accumulation being altogether due to geological 

 structure. 



An essential condition for the retention of the petroleum in the situations which 

 have been described, is that the reservoir must be covered by an impervious stratum, such 

 as a considerable thickness of shales, clays or marls to hold them down. When this is 

 not the case, or where the anticlinal fold has been too sharp and has become fissured, 



