Ch. IX.] 
FORMS OF THE SICILIAN VALLEYS > 
109 
altered their structure, just as dikes of lava render more crys- 
talline the stratified masses which they traverse, and obliterate 
all traces of their organic remains. 
Suppose some of these changes to have been superinduced 
upon subaqueous deposits underlying the tertiary formations of 
Sicily, it is important to reflect that in that case no geological 
proofs would remain of the era when the alterations had taken 
place; and if, at some future period, the whole island should be 
uplifted, and these rocks of fusion, together with the altered 
strata, should be brought up to the surface, it would not be 
apparent that they had assumed their crystalline texture in the 
newer Pliocene period. For aught that would then appear, 
they might have acquired their peculiar mineral texture at 
epochs long anterior, and might be supposed to have been 
formed before the planet was inhabited by living beings ; in- 
stead of having originated at an era long subsequent to the 
introduction of the existing species. 
CHANGES OF THE SURFACE DURING AND SINCE THE EMER- 
GENCE OF THE NEWER PLIOCENE STRATA. 
Valleys. — Geologists who are accustomed to attribute a great 
portion of the inequalities of the earth's surface to the excava- 
ting power of running water during a long series of ages, will 
probably look for the signs of remarkable freshness in the 
aspect of countries so recently elevated as the parts of Sicily 
already described. There is, however, nothing in the external 
configuration of that country which would strike the eye of the 
most practised observer, as peculiar and distinct in character 
from many other districts in Europe which are of much higher 
antiquity. The general outline of the hills and valleys would 
accord perfectly well with what may often be observed in re- 
gard to other regions of equal altitude above the level of the 
sea. 
It is true that, towards the central parts of the island where 
the argillaceous deposits are of great thickness, as around Cas- 
trogiovanni, Caltanjsetta, and Piazza, the torrents are observed 
