238 VALLEYS EXCAVATED SINCE CAVES WERE INHABITED. 
rhinoceroses, &c. whose remains we find in caves, and diluvial loam 
and gravel, is evident both from the fact that the outscourings of 
these valleys form the gravel in which such bones are for the most 
part embedded; and from the number of caves (once inhabited as 
dens) that have been intersected and laid open in the cliffs that 
flank their sides and narrow gorges. The present entrance of these 
caves is often a hole in an absolutely vertical precipice, which it 
is impossible to approach except by ropes or ladders, and which, 
therefore, could not have been accessible to the animals whose bones 
we find within, if the caves had originally terminated, as they do at 
present, in the face of a precipice; it follows therefore, that the 
creation of such precipices, and consequently of the valleys in 
question, was posterior to the time in which the beasts occupied these 
dens. See an illustration of this hypothesis in the three caves 
intersected by the gorge of the Esbach, at Plate XVIII: see also 
Plate XV., XVI., and XIX. 
Note. “ The effects of water upon the solid strata of the globe have been the subject 
of much geological debate; but it is now almost universally admitted, that valleys have 
been excavated by causes no longer in action,—contrary to the opinion of Dr. Hutton 
and Mr. Playfair, who maintained that they were formed by the long continued erosion of 
the streams which actually run through them. This question had been long since placed 
in a very convincing light by Hutchinson and his disciple Catcott; who have shown, that 
the surface at present furrowed by valleys must have been in many cases continuous; 
and this, in innumerable instances, where streams do not exist at all, (as every chalk down 
clearly shows), or where the existing streams are quite inadequate to the effect. Thus, 
in a series such as is here represented. 
e e e 
the portions of the beds, a, b, and c, at present detached from each other, must once 
have been continuous; d has only been partially cut through ; and e has been left un- 
