728 REPORT— 1889. 



deposits of pitch, of carboniferous shales, and asphalts 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 vapours, of larger diameter than the earth now has, was gradually 

 separated. The various vapours and gases which, diffused through each other, 

 formed at first an atmosphere round an imaginary centre, gradually assumed the 

 form of a liquid globe and exerted pressures incomparably higher than those which 

 we experience now at the base of our present atmosphere. According to Dalton's 

 laws, gases, when dift'used through each other, behave as if they were separate ; 

 hence the lighter gases would preponderate in the outer regionsof 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 circum- 

 ference would expand, perform work, would cool in consequence, and at some 

 period would assume the liquid or even the solid state, just as we find the vapour 

 of water dift'used 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 chemical changes ; and 

 the cooling of the vapours 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 vapours of which have high specific densities and high mole- 

 cular weights — that is to say, composed of elements having high atomic weights — 

 and that the heavier elementary substances would collect nearer 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 1 to 40, became 

 condensed, entered into every conceivable combination with each other, and pro- 

 duced substances the specific gravity of which averages about 2^, never exceeds 4, 

 and are found near the immediate surface of the globe. 



But the mean speci6c gravity of the earth as determined by MaskeljTie, 

 Cavendish, and others certainly exceeds 5, and consequently the inner portion of 

 our globe must be composed of substances heavier than those existing on the 

 surface, and such substances 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. Secondly, 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 ; and of all the elements, iron, with a specific gravity 

 exceeding 7, and with an atomic weight of 56, corresponds best with these require- 

 ments, for it is found in abundance on the surface of the earth ; and the spectroscope 

 has revealed the very marlied presence of iron in the sun, where it must be partly 

 in the fluid and partly in the gaseous state; and consequently iron in large masses 

 must exist in the earth ; so that the mean specific gravity of our planet may well 

 be 5, the value which has been determined by independent means. 



