108 Lord Greenock on the Coal Formation of the 
itself, of the pre-existence of a sufficient extent of dry land, 
clothed with a luxuriant tropical vegetation, to have supplied 
this detritus and these remains, and sufficiently elevated to have 
given rise to the rivers and torrents, by the action of which this 
transported matter must have been carried down into the lakes 
or estuaries, in which, to all appearance, such deposits were 
formed. Whether this land constituted groups of islands, ac- 
cording to the opinion of many geologists, or continents of great- 
er or less extent, which, by subsequent revolutions, have been 
either wholly or partially submerged by the existing sea, is not 
our present object to inquire; but, from the size and position of 
the fossil trees enveloped in many of the beds of this formation, 
and other phenomena connected with them, there appear to be 
strong grounds for inferring that the volume of water discharged 
by these rivers, and the magnitude of their estuaries, must have 
been much more considerable than would probably have been 
the case if they had been situated in small islands ; and the oc- 
currence of terrestrial plants, with the remains of fishes, and of 
mollusca, that had either been the inhabitants of fresh-water or 
of shallow seas, in the lowest beds of the series, which have after- 
wards been covered by other deposits more decidedly of a marine 
character, seems to shew, that, although the former might have 
been originally deposited in lakes, or on flat shores near the 
mouths of rivers, frequent alternations in the relative level of the 
sea and land may probably have taken place since, by which a 
corresponding succession of deposits, varying accordingly in the 
character of their organic remains, have been. produced. 
The intermixture, however, of organic remains of a fluviatile 
character, with those of marine fishes and shells, is very general 
throughout the coal-measures, and it is still doubtful whether 
any well-authenticated proof exists of any beds having yet been 
discovered in the carboniferous series, which, from their organic 
contents, could be pronounced to have had exclusively a fresh- 
water origin, unless an exception. should be found in the lime- 
