20 Principles of Geology. 
No one has carried his speculations on this subject so far as Dr. 
Hutton, who maintained that vallies were, in all cases, scooped out 
by the streams which run in them.* This is a characteristic part of 
~ his system of decaying and renewing worlds, and whoever views the 
minute, though not imperceptible effects of our rivers, need not cavil 
at the ample time he allows for their producing such effects as the 
denudation of vallies. But this opinion clashes so directly with plain 
facts, as to be wholly inadmissible. How can we apply such an hy- 
pothesis to those numerous vallies in the plains of chalk in Yorkshire, 
Wiltshire, and Dorsetshire, which have never carried water in the 
memory of ages, down which, indeed no trace of a channel can be 
seen? Yet they are branched like the vallies of other districts, have 
all their sinuosity of course, and regular declination, but the soil and 
stratum are too absorbent to be moistened by the most hasty rain. 
- The excavation of vallies can be ascribed to no other cause than a 
great flood of water which overtopped the hills, from whose summits 
those vallies descend. Such a flood, put in violent motion, might, 
we may suppose, by its currents and eddies, scoop hollows which af- 
terwards, on its retreat, would be extended in long comnected vallies. 
From the best and most independent evidence we have shewn, that 
such a flood has once overflowed the earth since the consolidation of 
its surface ; and as we have no proof of more than one such flood, 
and as there seems to be no contrary evidence, it is probably to the 
deluge we must ascribe the excavation of vallies. 
But the deluge has long passed away, and other events have ma- 
terially changed the face of the earth. Did not the voice of history 
and tradition teach us the great antiquity of that catastrophe, we yet 
might assure ourselves of it by the contemplation of nature. For 
when we find the dilavial deposits of clay, pebbles, and bones, cov- 
_ered by shell-mazrl, silt, peat, and large uprooted trees,—accumula- 
tions which proceed so slowly in our days, as to be hardly perceived 
in operation,—there is reason to conclude that along period sepa- 
rates us from the date of the deluge. And when, in these new accu- 
mulations, we find the bones of postdiluvian animals, which have be- 
come extinct through accident or persecution, as well as of others, 
Successors still exist in the neighborhood, we may, perhaps, 
Se ean Sa as NS oa Sn 
* . 
Quodque fuit campus, vallem decursus aguarum 
Petit, OVID, METAM. xy. 
