140 
NEWER PLIOCENE PERIOD. 
[Ch. XI. 
an extinct rhinoceros and hippopotamus, in a cave in the neigh- 
bourhood of Syracuse, where the country is composed entirely 
of the Val di Noto limestone. Some of the fragments in the 
breccia are perforated by lithodomi, and the whole mass is 
covered by a deposit of marine clay filled with recent shells *i 
These phenomena may, we think, be explained by supposing 
such oscillations of level as are known to occur on maritime 
coasts where earthquakes prevail, such, in fact, as have been 
witnessed on the shores of the Bay of Baiae within the last 
three centuries f. For it is evident that the temporary sub- 
mergence of a cave filled with osseous breccia might afford 
time for the perforation of the rock by boring testacea, and for 
the deposition upon it of mud, sand, and shells. 
The association in these and other localities of shells of living 
species with the remains of extinct mammalia is very distinct, 
and corroborates the inference adverted to in a former chapter, 
that the longevity of species in the mammalia is, upon the 
whole, inferior to that of the testacea. This circumstance we 
are by no means inclined to refer to the intervention of man, 
and his power of extirpating the larger quadrupeds, for the 
succession of mammiferous species appears to have been in like 
manner comparatively rapid throughout the older tertiary 
periods. Their more limited duration depends,, in all proba- 
bility, on physiological laws which render warm-blooded qua- 
drupeds less capable, in general, of accommodating themselves 
to a great variety of circumstances, and, consequently, of 
surviving the vicissitudes to which the earth's surface is ex- 
posed in a great lapse of ages^. 
Caves near Palermo. — The caves near Palermo exhibit ap- 
pearances very analogous to those above described, and much 
curious information has been lately published respecting them. 
According to Hoffmann, the grotto of Mardolce is distant 
about two miles from Palermo, and is 20 feet high and 10 
* Hoffmann, Archiv. fur Miueralogie, p, 393. Berlin, 1831. Dr. Christie, 
Proceedings of Geol. Soc, No. xxiii. p. 333. 
f Vol. i, chap. xxv. I See above, p. 48, and vol. i. chap. vi. 
