October 4, 1889.] 



SCIENCE. 



229 



the surface ; while in the superficial sands in which it is generally 

 found no one has ever discovered the presence of organized matter 

 in sufficiently large masses to have served as a source for the 

 enormous quantity of oil and gas yielded in some districts ; and 

 hence it is most probable that it has risen from much greater depths 

 under the influence of its own gaseous pressure, or floated up 

 upon the surface of water, with which it is so frequently associated. 



The oil-bearing strata in Europe belong chiefly to the tertiary or 

 later geological epochs ; so that it is conceivable that in these 

 strata, or in those immediately below them, carboniferous deposits 

 may exist, and may be the sources of the oil. But in America and 

 in Canada the oil-bearing sands are found in the Devonian and 

 Silurian formations, which are either destitute of organic remains 

 or contain them in insignificant quantities. Yet, if the immense 

 masses of hydrocarbons have been produced by chemical changes 

 in carboniferous beds, equally large masses of solid carboniferous 

 remains must still exist ; but of this there is absolutely no evidence 

 while cases occur in Pennsylvania where oil is obtained from the 

 Devonian rocks underlying compact clay-beds, on which rest coal- 

 bearing strata. Had the oil been derived from the coal, it certainly 

 would not have made its way downwards ; much less would it 

 have penetrated an impermeable stratum of clay. The conclusion 

 arrived at is, that it is impossible to ascribe the formation of naph- 

 tha to chemical changes produced by heat and pressure in ancient 

 organized remains. 



One of the first indices to the solution of the question lies in the 

 situation of the oil-bearing regions. They always occur in the 

 neighborhood of, and run parallel to, mountain ranges : as, for 

 example, in Pennsylvania, along the Alleghanies ; in Russia, along 

 the Caucasus. The crests of the ranges, formed originally of 

 horizontal strata which had been forced up by internal pressure, 

 must have been cracked and dislocated, the fissures widening out- 

 wards, while similar cracks must have been formed at the bases of 

 the ranges ; but the fissures would widen downwards, and would 

 form channels and cavities, into which naphtha, formed in the 

 depths to which the fissures descended, would rise and manifest 

 itself, especially in localities where the surface had been sufficiently 

 lowered by denudation or otherwise. 



It is in the lowest depths of these fissures that we must seek the 

 laboratories in which the oil is formed ; and, once produced, it 

 must inevitably rise to the surface, whether forced up by its own 

 pent-up gases or vapors, or floated up by associated water. In 

 some instances the oil penetrating or soaking through the surface 

 layers loses its more volatile constituents by evaporation, and in 

 consequence deposits of pitch, of carboniferous shales, and asphalt, 

 take place ; in other cases, the oil, impregnating sands at a lower 

 level, is often found under great pressure, and associated with 

 forms of itself in a permanently gaseous state. This oil may be 

 distributed widely, according to the nature of the formations or the 

 disturbances to which they have been subjected ; but the presence 

 of petroleum is not in any way connected with the geological age 

 of the oil-bearing strata, it is simply the result of physical condition 

 and of surface structure. 



According to the views of Laplace, the planetary system has been 

 formed from incandescent matter torn from the solar equatorial 

 regions. In the first instance, this matter formed a ring analogous 

 to those which we now see surrounding Saturn, and consisted of 

 all kinds of substances at a high temperature ; and from this mass 

 a sphere of vapors, of larger diameter than the earth now has, was 

 gradually separated. The various vapors and gases which, diffused 

 through each other, formed at first an atmosphere round an imagi- 

 nary centre, gradually assumed the form of a liquid globe, and 

 exerted pressures incomparably higher than those which we ex- 

 perience now at the base of our present atmosphere. According 

 to Dalton's laws, gases, when diffused through each other, behave 

 as if they were separate : hence the lighter gases would prepon- 

 derate in the outer regions of the vaporous globe, while the heavier 

 ones would accumulate to a larger extent at the central portion ; 

 and at the same time the gases circulating from the centre to the 

 circumference would expand, perform work, would cool in conse- 

 quence, and at some period would assume the liquid or even the 

 solid state, just as we find the vapor of water diffused through our 

 present atmosphere does now. That which is true of changes of 



physical condition, Henri St. Claire Deville, in his brilliant theory 

 of dissociation, has shown to be equally true with respect to chemi- 

 cal changes ; and the cooling of the vapors forming the earth while 

 in its gaseous condition was necessarily accompanied by chemical 

 combinations, which took place chiefly on the outer surface, where 

 oxides of the metals were formed ; and, as these are generally less 

 volatile than the metals themselves, they were precipitated on to 

 what there then was of liquid or solid of the earth, in the form of 

 metallic rain or snow, and were again probably decomposed, in part 

 at least, to their vaporous condition. The necessary consequence 

 of this action is that the inner regions of the earth must consist of 

 substances the vapors of which have high specific densities and 

 high molecular weights, — that is to say, composed of elements 

 having high atomic weights, — and that the heavier elementary sub- 

 stances would collect near the centre, while the lighter ones would 

 be found nearer the surface. Our knowledge of the earth's crust 

 extends but to an insignificant distance ; yet, as far as we do know 

 it, we find that the arrangement above indicated prevails. Hydrogen, 

 carbon, nitrogen, oxygen, sodium, magnesium, aluminium, silicon, 

 phosphorus, sulphur, chlorine, potassium, calcium, — substances 

 whose atomic weights range from i to 40, — became condensed, 

 entered into every conceivable combination with each other, and 

 produced substances the specific gravity of which averages about 

 2-i, never exceeds 4, and are found near the immediate surface of 

 the globe. 



But the mean specific gravity of the earth as determined by 

 JVlaskelyne, Cavendish, and others, certainly exceeds 5, and conse- 

 quently the inner portion of our globe must be composed of sub- 

 stances heavier than those existing on the surface ; and such sub- 

 stances are only to be found among the elements with high atomic 

 weights. The question arises, " What elements of this character 

 are we likely to find in the depths of the earth .' " In the first 

 place, since gases diffuse through each other, a certain proportion 

 of the elements of high atomic weight will also be found on the 

 surface of the earth. Second, the elements forming the bulk of the 

 earth must be found in the atmosphere of the sun — if, indeed, the 

 earth once formed part of its atmosphere. Of all the elements, 

 iron, with a specific gravity exceeding 7, and with an atomic weight 

 of 56, corresponds best with these requirements, for it is found in 

 abundance on the surface of the earth ; and the spectroscope has 

 revealed the very marked presence of iron in the sun, where it must 

 be partly in the fluid and partly in the gaseous state, and conse- 

 quently iron in large masses must exist in the earth : so that the 

 mean specific gravity of our planet may well be 5, the value of 

 which has been determined by independent means. 



It is not easy, however, to define in what condition the mass of 

 iron which exists in the heart of the earth is likely to be. Iron is 

 capable of forming a vast number of combinations, depending on 

 the relative proportion of the various elements present. Thus, in 

 the blast-furnace, oxygen, carbon, nitrogen, calcium, silicon, and 

 iron are associated, and produce under the action of heat, besides 

 various gases, a carburet of iron and slag, the latter containing 

 chiefly silicon, calcium, and oxygen ; that is to say, substances 

 similar to those which form the bulk of the surface of the earth. 

 But these same elements, if there be an excess of oxygen, will not 

 yield any carburet of iron ; and the same result will follow if there be 

 a deficiency of silicon and calcium, because of the large proportion 

 of oxygen which they appropriate. In the same way, during the 

 cooling of the earth, if oxygen, carbon, and iron were associated, 

 and if the carbon were in excess of the oxygen, the greater part of 

 the carbon would escape in the gaseous state, while the remaining 

 part would unite with the iron. It is certain that in the heart of 

 the earth there must have been a deficiency of oxygen, because of 

 its low specific gravity ; and the argument is supported by the fact 

 that free oxygen and its compounds, with the lighter elements, 

 abound on the surface. Further, it must be presumed that much 

 of the iron existing at great depths must be covered over and pro- 

 tected from oxygen by a coating of slag ; so that, taking all these 

 considerations into account, it is reasonable to conclude that deep 

 down in the earth there exist large masses of iron, in part at least 

 in the metallic state, or combined with carbon. 



The above views receive considerable confirmation from the com- 

 position of meteoric matter ; for it also forms a portion of the solar 



