HO NEWER PLIOCENE PERIOD. [Ch. IX^ 



annually to deepen the ravines in which they flow, and the tra- 

 veller occasionally finds that the narrow mule-path, instead of 

 winding round the head of a ravine, terminates abruptly in a 

 deep trench which has been hollowed out, during the preceding 

 winter, through soft clay. But throughout a great part of 

 Italy, where the marls and sands of the Subapennine hills are 

 elevated to considerable heights, the same rapid degradation is 

 often perceived. 



In the limestone districts of the Val di Noto, the strata are 

 for the most part nearly horizontal, and on each side of the 

 valley form a succession of ledges or small terraces, instead of 

 descending in a gradual slope towards the river-plain in the 

 manner of the argillaceous formations. When there is a bend 

 in the valley, the exact appearance of an amphitheatre with a 

 range of marble seats is produced. A good example of this 

 configuration occurs near the town of Melilli, in the Val di 

 Noto, as seen in the annexed view (No. 22). In the south of 



No. 22. 



Valley called Goxzo degli Martin, Mow Melilli. 



the island, as near Spaccaforno, Scicli and Modica, precipitous 

 rocks of white limestone, ascending to the height of five hun- 

 dred feet, have been carved out into the same form. 



A careful examination of the mode of decomposition of the 

 rock would be requisite, in order fully to explain this pheno- 

 menon. There is probably a tendency to a vertical fracture in 



