548 



SCIENCE. 



[N. S. Vol. XX. Xo. .513. 



lowed by Lord Kelvin in view of the uncer- 

 tainty of this datum. 



The researches of Kelvin and Darwin, 

 supplementing those of Kant and others, 

 have left no doubt that the moon was for- 

 merly closer to the earth than it now is, 

 and that the rotation of the latter was more 

 rapid, involving a greater ellipticity of the 

 meridian than it now shows. In a fluid or 

 Cartesian earth the change of ngure might 

 have produced little effect on the struc- 

 ture of the planet. If the earth is chiefly 

 a mass of crystalline nickel steel, it is very 

 possible that such a change in the figure of 

 equilibrium might rupture it. Since the 

 epoch at which the earth rotated in 5 hours 

 30 minutes, the polar axis must have elon- 

 gated by several per cent., most of it before 

 the time of rotation was reduced to 11 

 hours.* Were the earth chiefly composed 

 of forged steel, such elongation might be 

 produced by plastic deformation; but me- 

 teoric iron is rather comparable with cast 

 iron, or better still, with relatively brittle, 

 unforged cement steel, and might break. 



Now it is an indubitable fact that a ma- 

 jority of the outlines of the great oceanic 

 basins and of the chief tectonic lines of the 

 globe, lie nearly on great circles tangent to 

 the Arctic Ocean and to the Antarctic con- 

 tinent.! These lines, or most of them, are 



* Compare Thompson and Tait, ' Nat. Phil.,' 

 § 772, where the rotational period and eccentricity 

 are given for a fluid of the mass of the earth and 

 possessing its mean density. When the period is 

 5h. 30m., this table gives the data for computing 

 that the polar axis has a length equal to 0.95 of 

 the length vi^hich it has when the period is a 

 siderial day. For rotation in lOh. 57m. the polar 

 axis is 0.99 times that for a day. 



t In 1857 Professor R. Owen, of Tennessee, and, 

 independently, Benjamin Peirce, called attention 

 to the tangeney of the coast lines to the polar 

 circles (not to the coast lines of the arctic sea 

 and the antarctic continent), each attributing the 

 facts to the influence of the sun. In the first 

 ' Yearbook ' of the Carnegie Institution I failed 

 to refer to these publications. 



of extremely high geological age, their main 

 features having found expression as early 

 as the oldest known fossils and in some 

 eases still earlier. It appears to me very 

 possible that these fundamental ruptures 

 of the globe were due to the change of 

 figure attendant upon diminution of the 

 earth's period of rotation. Their symmet- 

 rical disposition with reference to the polar 

 axis is unquestionable, as well as the fact 

 that they penetrate to great depths. They 

 must be due to some tremendous force 

 acting axially, which actually altered the 

 eUiptieity of the meridian, since these fis- 

 sures could not have been formed without 

 modifying the shape of the globe, and the 

 only known disturbance of this description 

 is the change of figure referred to. On the 

 other hand, were the earth homogeneous, 

 such ruptures would be expected to have as 

 envelopes small circles in latitude 45° in- 

 stead of at about latitude 70°. But since 

 the earth is not homogeneous, this discord- 

 ance does not invalidate the suggestion. 



Be this as it may, upheavals, subsidences 

 and attendant contractions have been in 

 progress throughout the whole of historical 

 geology or the period within which fossils 

 afi'ord a guide to the succession of strata. 

 The so-called contractional theory has 

 shown itself wholly inadequate to account 

 for the amount of deformation traceable 

 in the rocks of the globe, nor has the ex- 

 travasation of igneous rock been sufficient 

 to account for the phenomena. To me the 

 earth appears to be a somewhat imperfect 

 heat engine in which the escape of thermal 

 energy is attended by the conversion of a 

 part of the supply into the vast amount 

 of molar energy manifested in the upthrust 

 and crumpling of continents. The subject 

 will probably turn out to be accessible 

 mathematically after certain experimental 

 determinations have been made, and I shall 

 return to it presently. 



Orogeny or mountain building is a mere 



