20 Principles of Geology. 



No one has darried 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 w^e 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 w^ater 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 v/hich af- 

 terwards, on its retreat, would be extended in long connected vallies. 

 From the best and most independent evidence w^e have shew^n, 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 y^t 

 might assure ourselves of it by the contemplation of nature. For 

 when we find the diluvial deposits of clay, pebbles, and bones, cov- 

 ered by shell-marl, 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 a long 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, 

 whose successors still exist in the neighborhood, we may, perhaps, 



'■' Quodque fuit campus, vallem decursus aqnarum 



Fecit. OVID, METAM. XV. 



