June 25, 1886.] 



SCIENCE. 



561 



tillation has ever been applied, least of all that 

 it is being applied, to Ohio rocks. The claim is * 

 sometimes made for an agency of manufacture 

 called • spontaneous distillation ; ' but. so far as 

 can be seen, this is a human invention, and not a 

 natural process. Instead of furnishing an expla- 

 nation, it begs the question at issue. Destructive 

 distillation we know, and chemical decomposition, 

 in its various phases, we know : but what is 

 ' spontaneous distillation ' as an agency for the 

 formation of petroleum from organic matter ? 



4. The wide diffusion of petroleum and its 

 derivatives is well illustrated by the facts recently 

 developed in Ohio. It is a mistaken view that 

 these substances are of rare occurrence. Valuable 

 accumulations, of course, are rare, but their pres- 

 ence in measurable quantity is well-nigh universal 

 in the paleozoic rocks of the Mississippi valley. 

 Prof. N. W. Lord, chemist of the Ohio geological 

 survey, has recently examined the black shale of 

 the state with this reference. He finds in normal 

 shale more than two-tenths of one per cent of 

 heavy oil. This amount he has weighed, but, 

 from the nature of the processes he was obliged to 

 use, he is certain that he has not obtained all that 

 was present in the shale. Petroleum as such, or 

 compounds derived from petroleum, as asphaltic 

 grains or films, are also found in all of our princi- 

 pal limestones. Dr. Hunt reported, a number of 

 years ago, more than four per cent of petroleum, 

 or bituminous matter which was undoubtedly de- 

 rived from petroleum, in the Niagara limestone of 

 Bridgeport, near Chicago. These figures can be 

 duplicated in some phases of the upper Silurian 

 limestones of Ohio. 



5. The amount of petroleum stored in the rocks 

 is seen to be enormous. Take the figures of Pro- 

 fessor Lord, already quoted. Two-tenths of one 

 per cent of petroleum in a rock represents more 

 than twenty thousand barrels to the square mile 

 for every foot in depth. But the black shale is on 

 its outcrop three hundred feet in thickness, and 

 in the interior the formation is from four to six 

 times as thick. Three hundred feet of shale would 

 contain, to the square mile, six million barrels of 

 petroleum. Suppose the rate given above is too 

 high : divide it by two, by four, by eight, and 

 even the last result would show nearly as much 

 petroleum as has ever been taken from any square 

 mile of the Pennsylvania fields. 



6. The old dispute as to whether petroleum is 

 mainly derived from bituminous shales or bitumi- 

 nous limestones has become ' a past issue,' largely 

 through recent developments in Ohio. No ques- 

 tion relating to the geology of petroleum has been 

 more warmly or ably discussed. As so often 

 iiappens, both sides were right in their main affir- 



mations, and both were wrong in what they de- 

 nied. The petroleum and gas of eastern Ohio, 

 and, by the same token, of western Pennsylvania 

 and New York, are unquestionably derived from 

 the great shale formation of Devonian and sub- 

 carboniferous age that underlies this territory, 

 and they are stored in sandstones overlying or 

 interstratified with these shales. The petroleum 

 and gas of north-western Ohio are as certainly de- 

 rived from good normal Trenton limestone that is 

 at least five hundred feet thick, and underneath 

 which no shales are known to exist. 



That the oil and gas of eastern Ohio are derived 

 from the shales, and not from the sandstones in 

 which they are now found, becomes evident from 

 the fact already noted ; viz. , that the underlying 

 shales always contain a measurable amount of 

 petroleum, while the Berea grit, which is the 

 main Ohio reservoir, is everywhere, in outcrop 

 and under deepest cover, a clean, sharp sandstone, 

 remarkably free from organic remains of all de- 

 scription. Ex nihilo, nihil fit. If the source of 

 oil were to be foimd in a sandstone containing 

 organic remains, the Logan conglomerate (Pocono) 

 should be a much more productive rock than the 

 Berea grit. It is ten times as thick, and several 

 times as coarse, and contains a profusion of sand- 

 stone casts of tree-trunks ; but it is underlain 

 with light-colored instead of black shale. It is 

 the great salt-water sand of eastern Ohio, and is 

 but rarely petroliferous on any considerable scale. 



7. The gas and oil derived from bituminous 

 shales are found to differ in composition, to some 

 extent, from limestone oil and gas. In particular, 

 the latter are never free from small percentages of 

 sulphur compounds, none of which appear in the 

 gas or oil of the shale. These compounds adver- 

 tise themselves wherever they occur, and make 

 the most noticeable characteristic of these oils. 



The composition of Pittsburg gas is reported 

 as very variable, even from the same well. All 

 the observations on the limestone gas of Ohio 

 show it to be remarkably steady and uniform. 



Mr. S. A. Ford, chemist of the Edgar Thompson 

 steel-works, gives a number of important facts 

 concerning the composition of Pennsylvania gas 

 in a recent number of the American manufacturer 

 (Natural gas supplement, April, 1886). He gives 

 the composition of what he counts average Pitts- 

 burg gas, as follows : — 



Pittsburg gas. 



Hydrogen 22.00 



Marsh-gas 67.00 



Ethylic hydride 5.00 



defiant gas 1.00 



Nitrogen 3.00 



Carbonic acid 0.60 



Carbonic oxide 0.60 



Oxygen 0.80 



