240 
MR. C. DAVISON ON THE DISTRIBUTION OP STRAIN IN THE 
surface of a once viscous Earth by “ the diminution of oblateness arising from the 
diminished velocity of rotation upon the axis ” resulting from tidal friction; wrinkles 
that would be amply large enough to form the foundations of the continental masses. 
In order to prove the insufficiency of the contraction theory, it is necessary, therefore, 
to show that folding by lateral pressure, both directly and indirectly, by acting on 
vast masses of sediment, is incapable of producing, not the average height of the 
inequalities of the Earth’s surface, but the total amount of rock-folding in all past and 
present mountain-chains. 
III. The Effects of Crust-Stretching and Folding on the Evolution of the Earth’s 
Surface-Features. 
(20) It has been already stated that much weight cannot be attached to the 
numerical results obtained in this paper. They are evidently dependent on the 
assumptions made at the commencement. It should also be remembered that the 
coefficient of expansion (e) has been supposed constant at whatever temperature the 
loss of heat takes place, and there is reason for believing that this is not strictly true. 
And again, it was assumed that, on solidifying, the surface of the Earth was a smooth 
sphere, although by the interference of tidal friction there must previously have been 
raised up masses forming the nuclei which, by continual growth of folded rock and 
mountain-range along their borders, have developed into our present continental 
areas. Clearly the existence of these great masses from the very beginning must 
have had an all-important influence on the subsequent evolution of the Earth’s surface- 
features. 
(21) “In the case of the Earth,” says Professor G. H. Darwin, “'the wrinkles 
would run north and south at the equator, and would bear away to the eastward in 
northerly and southerly latitudes ; so that at the north pole the trend would be 
north-east, and at the south pole north-west. Also the intensity of the wrinkling 
force varies as the square of the cosine of the latitude, and is thus greatest at the 
equator, and zero at the poles. Any wrinkle when once formed would have a 
tendency to turn slightly, so as to become more nearly east and west than it was 
when first made. 
“ The general configuration of the continents (the large wrinkles) on the Earth’s 
surface appears to me remarkable when viewed in connection with these results.” 
And again, indicating a physical cause of continental permanence, he says, “ But, if 
this cause was that which principally determined the direction of terrestrial inequalities, 
then the view must be held that the general position of the continents has always 
been somewhat as at present, and that, after the wrinkles were formed, the surface 
attained a considerable rigidity, so that the inequalities could not entirely subside 
during the continuous adjustment to the form of equilibrium of the Earth adapted at 
each period to the lengthening day. With respect to this point it is worthy of remark 
