26 Proceedings of the Royal Physical Socvety. 
crust under the tangential stress caused by progressive radial 
contraction, and the one is complementary to the other. 
Each continent is the arched ridge of a primary earth-fold, 
while the contiguous ocean is the complementary trough of 
the same—so that the formation of the one implies the 
formation of the other. But there is nevertheless —as 
pointed out by Suess (Natural Science, vol. ii, 1893) —a 
marked difference between the types of movement to which 
continents and ocean-basins respectively owe their existence. 
The continents are essentially the result of the ridging up of 
a portion of the earth’s crust in a series of parallel folds. On 
the other hand, the ocean-basins are the result of the settling 
down (“sagging down ” or “ effondreiment ”) of larger or smaller 
areas, more or less as a whole. “The descent of a con- 
siderable area, forming a large new depression, demands a 
certain part of the existing volume of oceanic waters for the 
filling of the new depth. The consequence is, the sinking of 
the oceanic surface all over the planet, and the apparent step- 
like rising of coast-lines. Thus is explained the apparently 
episodic elevation of whole continents, without any disturb- 
ance of horizontality, or the least alteration of the net of 
water-courses spread over the land. It is in this sense alone 
that a certain balance of ‘elevation’ and ‘subsidence’ might 
be conceded” (Suess, op. cit., supra). Without pursuing this 
argument further, it is sufficient to point out that, owing to 
the different nature of the movements by which continents 
and ocean-basins are respectively produced, we cannot 
assume, with Mr Wallace, that “on any large scale elevation 
and subsidence must nearly balance one another.” If it be 
admitted that the ridging up of a continent is accompanied 
by the “sagging down” of a contiguous area, it would seem 
tolerably certain that the subsidence of a continent would 
cause the ridging up of a neighbouring ocean-basin; and we 
have no grounds for assuming that the two processes would 
exactly balance one another. On the contrary, there are 
strong grounds for believing that in two contiguous areas 
undergoing relative displacement, the amount of the folding 
and ridging up of the one would be much greater than the 
“ sagging down.” of the other. 
