282 DYNAMICAL GEOLOGY.  [Boox II 
sink tranquilly under the sea, that fragments of that surface may be ~ 
preserved under overlying marine accumulations. It is in such 
places that “submerged forests” occur. These are stumps of trees 
still in their positions of growth in their native soil, often associated 
_ with beds of peat, full of tree-roots, hazel-nuts, branches, leaves, and 
other indications of a terrestrial surface. 
De la Beche has described, round the shores of Devon, Cornwall, 
and western Somerset, a vegetable accumulation, consisting of plants 
of the same species as those which now grow freely on the adjoining ~ 
land, and occurring as a bed at the mouths of valleys, at the bottoms — 
of sheltered bays, and in front of and under low tracts of land, of 
which the seaward side dips beneath the present level of the sea.’ 
Over this submerged land-surface sand and silt containing estuarine 
shells have generally been deposited, whence we may infer that in 
the submergence the valleys first became estuaries, and then sea- 
bays. If now, in the course of ages, a series of such submerged 
forests should be formed one over the other, and if, finally, they 
should, by upheaval of the sea-bottom, be once more laid dry, so as 
to be capable of examination by boring, well-sinking, or otherwise, 
they would prove a former long-continued depression, with intervals 
of rest. These intervals would be marked by the buried forests, and 
the progress of depression by the strata of sand and mud lying between 
them. In short, the evidence would be strictly on a parallel with 
that furnished by a succession of raised beaches as to a former 
protracted intermittent elevation, 
Coral-islands.—Hvidence of wide-spread depression, over the 
area of the Pacific and Indian Oceans, has been adduced from the 
structure and growth of coral reefs and islands. Mr. Darwin, many 
years ago, pointed out that as the reef-building corals do not live at — 
depths of more than 20 to 30 fathoms, and yet their reefs rise 
out of deep water, the sites on which they have formed those 




structures may be conceived to have subsided, the rate of subsidence _ 
being so slow, that the upward growth of the reef has on the whole 
kept pace with it.2 The formation of coral-reefs is described in 
Book III. Part IL. Section iii, and Mr. Darwin’s theory is there 
more fully explained. 
Distribution of plants and animals.—Since the appear- 
ance of Hdward Forbes’s essay upon the connection between the 
distribution of the existing fauna and flora of the British Isles, and 
the geological changes which have affected their area,? much atten- 
tion has been given to the evidence furnished by the geographical 
distribution of plants and animals as to geological revolutions, In 
some cases the former existence of land now submerged has been 
inferred with considerable confidence from the distribution of living 
1 “Geology of Devon and Cornwall,” Mem. Geol. Survey. For further accounts of 
British submerged forests see Q. J. Geol. Soc. xxii. p. 1; xxxiv. p. 447. Geol. Mag. vi. 
p. 76; vii. p. 645 1. 2ud ser. p. 491; vi. pp. 80, 251. 
2 See Darwin's Coral Islands, also Dana’s Corals and Coral Islands. 
% Mem, Geol. Survey, vol. i, 1846, p. 386, 
