128 
THEORY OF THE FORMATION 
Ch. V. 
parts of the great oceans might become interspersed 
with coral-islets, none of which would rise to a greater 
height than that attained by detritus heaped up by the 
sea, and nevertheless they might all have been formed 
by corals, which absolutely require for their growth a 
solid foundation within a few fathoms of the surface. 
It would be out of place here to do more than 
allude to the many facts, showing that the supposition 
of a gradual subsidence over large areas is by no means 
improbable. We have the clearest proof that a move- 
ment of this kind is possible, in the upright trees 
buried under strata many thousand feet in thickness ; 
we have also every reason for believing that there are 
now large areas gradually sinking, in the same manner 
as others are rising. And when we consider how many 
parts of the surface of the globe have been elevated 
within recent geological periods, we must admit that 
there have been subsidences on a corresponding scale, 
for otherwise the whole globe would have swollen. It 
is very remarkable that Sir C. Lyell, 1 even in the first 
edition of his Principles of Geology, inferred that the 
amount of subsidence in the Pacific must have exceeded 
that of elevation, from the area of land being very 
small relatively to the agents there tending to form, it, 
namely, the growth of coral and volcanic action. But, 
although subsidence may explain a phenomenon other- 
wise inexplicable, it may be asked, are there any direct 
proofs of a subsiding movement in these areas ? This, 
1 Principles of Geology, sixth edition, vol. iii. p. 386. [Ch. xlix. 
vol. ii. p. 604, eleventh edition.] 
