270 
EOCENE PERIOD. 
[Ch. XIX. 
same may be said of those of Velay. Until the bones of men 
or articles of human workmanship are found buried under 
some of their lavas, instead of the remains of extinct animals, 
which alone have hitherto been met with, we shall consider it 
probable, as we before hinted, that the latest of the volcanic 
eruptions may have occurred during the Miocene period. 
Supposed effects of the Flood. 
They who have used the terms ante-diluvian and post- 
diluvian in the manner above adverted to, proceed on the 
assumption that there are clear and unequivocal marks of the 
passage of a general flood over all parts of the surface of the 
globe. It had long been a question among the learned, even 
before the commencement of geological researches, whether the 
deluge of the Scriptures was universal in reference to the whole 
surface of the globe, or only so with respect to that portion of 
it which was then inhabited by man. If the latter interpreta- 
tion be admissible, the reader will have seen, in former parts of 
this work, that there are two classes of phenomena in the con- 
figuration of the earth's surface, which might enable us to 
account for such an event. First, extensive lakes elevated above 
the level of the ocean ; secondly, large tracts of dry land de- 
pressed below that level. When there is an immense lake, having 
its surface, like Lake Superior, raised 600 feet above the level 
of the sea, the waters may be suddenly let loose by the rend- 
ing or sinking down of the barrier during earthquakes, and 
hereby a region as extensive as the valley of the Mississippi, 
inhabited by a population of several millions, might be de- 
luged *i On the other hand, there may be a country placed 
beneath the mean level of the ocean, as we have shown to be the 
case with part of Asia -f*, and such a region must be entirely laid 
under water should the tract which separates it from the ocean 
* See vol. i. p. 89, and Second Edition, p. 101. 
f Vol. ii. p, 163, and Second Edition, p. 169. 
