25"8 W. B. Taylor — Crumpling of the Earth's Crust. 



solidification of our planet since its present form has been 

 reached, requires a notice here, rather from the character of its 

 source, than from its own intrinsic force or importance. 



Professor "William Thomson, adopting Mr. Adams' estimate 

 of tidal retardation, thus argues : " If the rate of retardation had 

 been uniform since ten million centuries back, the earth must 

 have been then rotating faster by one-seventh than at present, 

 and the centrifugal force greater in the proportion of 64 to 49. 

 If the consolidation took place then, or earlier, the ellipticity 

 of the upper layers of equal density must have been yts instead 

 of about 3-A-J5- as it certainly now is. It is impossible to escape 

 the conclusion that the date of the consolidation is considerably 

 more recent than a thousand million years ago.* 



Professor Peter Gr. Tait (as if not to be outdone), is still 

 more emphatic and positive in his enunciation. He says : " It 

 being thus established that the rate of rotation of the earth is 

 constantly becoming slower the question comes : How long ago 

 must it have solidified in order that it might have the partic- 

 ular amount of polar flattening which it shows at present? 

 Suppose, for instance, it had not consolidated less than a 

 thousand million years ago. Calculation shows us that at that 

 time, on the most moderate computation, it must have been 

 rotating at least twice as fast as it is now rotating. That is to 

 say, the day must have been 12 hours long instead of 24. 

 Now if that had been the case, and the earth still fluid 

 throughout, or even pasty, that double rate of rotation would 

 have produced four times as great centrifugal force at the 

 equator as at present, and the flattening of the earth at the 

 poles and the bulging at the equator would have been much 

 greater than we find them to be. We say then, that because 

 the earth is so little flattened it must have been rotating at 

 very nearly the same rate as it is now rotating, when it became 

 solid. Therefore, as the rate of rotation is undoubtedly becom- 

 ing slower and slower, it cannot have been many millions of 

 years back when it became solid, else it would have solidified 

 into something very much flatier than we find it."f 



The supposition that a granite mountain or equatorial pro- 

 tuberance 400 miles high or 100 miles high, could for a 

 moment support itself would hardly be entertained by a prac- 

 tical civil engineer.^: 



It is now nearly forty years since Herbert Spencer, with a 

 juster physical insight, contended and satisfactorily showed 

 that a solid earth (of any shape) would assume the oblate 



* Nat. Philos., 1867, vol. i, Sec. 830, p. 687. 



f Lect. on recent advances in Phys. Sci., 1876, lect. vii, pp. 173, 174. 

 % The limiting modulus of height of a granite pyramid (equaling one side of 

 its square base), is somewhat less than eleven miles. 



