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, Caltanisetta, and Piazza, the torrents are observed 



