179 
land, and a corresponding variation in the ratio of land 
to sea in the northern hemisphere, has been a principal 
agent, assisted, as it necessarily would be, by a consequent 
change in minor physico-geographical phenomena. The 
hypothesis that those vast masses of vegetable remains 
which form our coal fields have been transported from 
foreign climes by the overwhelming agency of large bodies 
of moving water, cannot, I think, be maintained, when 
the position of the flora, and the angular shape and large 
size of the particles of rock with which they are associated, 
are accurately observed. The rich supplies of carbonic 
acid from the atmosphere, and the fresh unimpaired soils 
of the period, formed the sustenance of vast forests which 
flourished for a long series of years with extraordinary 
vigour. 
The districts, however, whose elevation above the sea 
level had introduced such remarkable modifications in the 
climate, rested on no secure foundation, and during sub- 
sequent disturbances seem to have been again submerged. 
The existence of the alternating freshwater beds of coal 
and strata, from the shells they contain, evidently marine, 
indicates that these convulsions were more gradual than 
the preceding elevations; and that while the depressions 
appear to have been local, and the area of water confined 
to the valleys, the mountains and higher lands projecting 
above the sea formed an ocean studded with islands. These 
islands, after the erosion of their sides had furnished mate- 
rial for the marine deposits alluded to, again, by a series 
of gradual elevations and depressions, assumed the form 
of a new and vast continent, whose soil, vegetation, and 
climate, had been transformed into our own. The ancient 
forests, thus imbedded in the marine deposits with which 
we now find them associated, underwent a process of erema- 
causis or decay, varying in its nature with the depth of 
