238 
MR. C. DAVISON ON THE DISTRIBUTION OF STRAIN IN THE 
amount folded in a given time is very nearly constant, but in reality slightly 
diminishing as the time increases. 
Hence the ratio of the areas contained hy the parts of the continuous curve in the 
figure with the axis Ox, to the right and left of that axis, may be considered to 
represent roughly the ratio of the total amount of rock stretched to the total amount 
folded since the earth solidified. 4 ’" 
II, The Rev. O. Fisher’s Argument on the Insufficiency of the Contraction Theory. 
(16) It may he well here to refer to the objection urged against the contraction 
theory by the Rev. 0. Fisher, an objection which has by some been considered 
conclusive against either the contraction theory, as usually held, or the assumptions on 
which that theory is founded. In its latest form this argument will be found in 
a paper in the ‘Philosophical Magazine’ for February, 18 8 7.t Briefly it may be 
summed up as follows 
Mr. Fisher’s argument is based on the assumptions that, initially, the Earth was 
practically solid, its surface spherical, and its whole mass at the high temperature of 
7000° F. throughout; and that it cooled down from this condition to that implied by 
Sir W. Thomson’s solution. Further, he takes the case which he considers most 
favourable to the advocates of the contraction theory, and supposes that each 
spherical layer, in sinking down by reason of the cooling of the mass beneath, 
maintained its horizontal extension, so that the whole of the compression, introduced 
by its having to fit on the shrunken nucleus, was rendered available for producing 
corrugations. He thus finds that “if all the elevations which would have been 
produced by compression, through the contraction of the Earth cooling as a solid, were 
levelled down, they would form a coating of about 900 feet in thickness above the 
datum level, which would be the surface, had the matter of the crust been perfectly 
compressible, so that compression would not have corrugated it.” He concludes, 
therefore, that, “ if we take into consideration the land and the ocean-basins, the 
existing inequalities of the surface are greater than can be accounted for by the 
theory of compression through contraction by cooling of a solid globe, even upon the 
too highly favourable suppositions made in the present paper. 
This argument seems to me inconclusive on several grounds. 
* Roughly, this ratio is about 340 to 1. But this relates only to folding resulting directly from 
secular cooling, the surface of the Earth being smooth and spherical. The total amount of rock-folding 
must, of course, be far in excess of that indicated by this ratio; see footnote to § (23). 
f “ On the Amount of the Elevations attributable to Compression through the Contraction during 
Cooling of a Solid Earth,” ‘ Phil. Mag.,’ vol. 23, 1887, pp. 145-149. The original form of the argument 
is contained in a paper “ On the Inequalities of the Earth’s Surface viewed in connection with the 
Secular Cooling,” ‘ Cambridge Phil. Soc. Trans.,’ vol. 12, 1879, pp. 414-433, and in ‘ The Physics of the 
Earth’s Crust’ (1881), chaps, v. and vi. See also a letter to ‘ Nature,’ Nov. 23, 1882 (vol. 27, pp. 76-77). 
+ ‘ Phil. Mag.,’ vol. 23, 1887, pp. 148-149. 
