Origin of Continents. 
481 
Darwin, 1 apparently also working on the hypothesis that the 
continents were formed after the earth became somewhat rigid, 
suggests that the protrusion of the continental masses is due 
to the tides. The secular distortion consequent upon tidal action 
due to inertia would result in " screwing action ” upon the earth. 
" Now this sort of motion, acting on a mass which is not per¬ 
fectly homogeneous, would raise wrinkles on the surface which 
would run in directions perpendicular to the axis of greatest 
pressure. In the case of the earth 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 northeast, and at the south pole 
northwest. 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. There can be little doubt that, 
on the whole, the highest mountains are equatorial, and that 
the general trend of the great continents is north and south in 
those regions. The theoretical directions of coast line are not 
so well marked in parts removed from the equator." He further 
concludes that if this be a correct explanation “ 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 ad. 
justment to the form of equilibrium of the earth, adapted at 
each period to the lengthening day. ” 
As has been seen, geologists would not agree that the conti¬ 
nental masses are sustained by their own strength. However, 
this tendency to produce wrinkles might work in connection 
with the tendency for lighter materials first to segregate, with 
1 Problems connected with the tides of a viscous spheroid, by G. H. Dar¬ 
win: Phil. Trans. Roy. Soc., Vol. 170, 1879, Part 2, pp. 587-590. 
31 
