Great Valley of the Scottish Lowlands. 117 
' Mr De La Becug, in a recent work on theoretical geology, * 
from a consideration of the facts connected with these coal-mea- 
sures, is led to the conclusion, that, at the period when the carbo- 
niferous limestone of the south of England was produced in the 
sea, there was probably dry land in the part of the European 
area not far to the northward of the present Tweed, and that a 
gradual rise of the land was effected, by which means terrestrial 
vegetation travelled farther to the south, so that its remains be- 
came abundantly entombed in that direction, producing the coal 
now found in Southern England and Wales, as also in Belgium 
and Northern France, the continuity of the whole being super- 
ficially concealed by the more recent secondary and tertiary de- 
posits of those countries. 
But, as Mr De xa Becue so justly and eloquently adds, + 
“ To trace even the probable positions of dry land over the Eu- 
ropean area at the carboniferous epoch, would be most difficult, 
particularly when we recollect that what we term a geological 
epoch, may include a long series of ages, and that thus land may 
rise and fall, be degraded and replaced, sometimes by the same, 
sometimes by greater, intensities of various forces than those the 
effects of which we daily witness, and yet the whole be included 
in a geological epoch, or rather one during which a particular 
group of rocks has been formed.” 
* Geological Researches, p. 318. + Ibid. p. 322. 
