Ch. V. 
OF QPRAL-EEEFS. 
125 
great banks of sediment, -which did not quite reach 
the surface owing to the action of superficial currents, 
aided possibly by the undulatory movement of the 
sea. This appears actually to have been the case in 
some parts of the West Indian sea. But in the form 
and disposition of the groups of atolls, there is nothing 
to countenance this notion ; and the assumption that 
a number of immense piles of sediment have been 
heaped on the floor of the great Pacific and Indian 
Oceans in their central parts, far remote from land, 
where the dark blue colour of the limpid water 
bespeaks its purity, cannot for one moment be 
admitted . 1 
The many widely scattered atolls must, therefore, 
rest on rocky bases. But we cannot believe that a 
broad mountain summit lies buried at the depth of 
a few fathoms beneath every atoll, and nevertheless 
that throughout the immense areas above-named, not 
one point of rock projects above the level of the sea. 
For we may judge of- mountains beneath the sea by 
those on the land ; and where can we find a single 
chain, much less several such chains, many hundred 
1 [This accumulation, it will be observed, is an integral part of Mr. 
Murray’s hypothesis. See Appendix II. for a sketch of the arguments 
by which it is supported. Perhaps I may be permitted to add that, 
in my opinion, the perusal of the observations of Mr. Murray, Mr. 
Guppy, and others would probably have led Mr. Darwin to modify 
slightly some of the clauses in these pages, and allow a more important 
r6le to the accumulation of organisms, other than corals, on submarine 
banks. I do not, however, anticipate that they would have seriously 
modified his general conclusions, or led him to regard modes of 
formation, which these authors consider to be normal, as other than 
exceptional.— T. G. B.] 
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