VALLEYS EXCAVATED BY DILUVIAN WATERS. 
237 
then laid bare by the sweeping away of the solid materials that had 
before filled them, are called valleys of denudation; and the effects 
we see produced by water in the minor cases I have just mentioned, 
by presenting us an example within tangible limits, prepare us to 
comprehend the mighty and stupendous magnitude of those forces, 
by which whole strata were swept away, and valleys laid open, and 
gorges excavated in the more solid portions of the substance of the 
earth, bearing the same proportion to the overwhelming ocean by 
which they were produced, that modern ravines on the sides of 
mountains bear to the torrents which since the retreat of the deluge 
have created and continue to enlarge them. 
When a gorge or valley takes its beginning, and continues its 
whole extent within the area of strata that are horizontal, or nearly 
so, and which bear no mark of having been moved from their original 
place by elevation, depression, or disturbance of any kind; and when 
it is also inclosed by hills that afford an exact correspondence of oppo¬ 
site parts, its origin must be referred to the removal of the substances 
that once filled it: and as it is quite impossible that this removal could 
have been produced in any conceivable duration of years by rivers that 
now flow through them, (since all the component streams, and conse¬ 
quently the rivers themselves, which are made up of their aggregate, 
owe their existence to the prior existence of the valleys through 
which they flow,) we must attribute it to some cause more powerful 
than any at present in action, and the only admissible explanation 
that suggests itself is, that they were excavated by the denuding 
force of a transient deluge. 
That these excavations took place at a period subsequent to that 
at which the earth was inhabited by the hyaenas, bears, elephants, 
