Ch. VI.] 



SICILY VAL DI NOTO. 73 



portion of these banks, so that nearly horizontal layers may 

 have been superimposed unconformably, after which another 

 bank may have been formed in a similar manner to the first. 



Volcanic conglomerates. In the Val di Noto we sometimes 

 meet with conglomerates entirely composed of volcanic pebbles. 

 They usually occur in the neighbourhood of masses of lava, 

 and may, perhaps, have been the shingle produced by the 

 wasting cliffs of small islands in a volcanic archipelago. The 

 formation of similar beds of volcanic pebbles may now be seen 

 in progress on the beach north of Catania, where the waves 

 are undermining one of the modern lavas of Etna ; and the 

 same may also be seen on the shores of Ischia. 



Proofs of gradual accumulation. In one part of the great 

 limestone formation near Lentini, I found some imbedded vol- 

 canic pebbles, covered with full-grown serpulse, supplying a 

 beautiful proof of a considerable interval of time having elapsed 

 between the rounding of these pebbles and their inclosure in a 

 solid stratum. I also observed, not far from Vizzini, a very 

 striking illustration of the length of the intervals which occa- 

 sionally separated the flows of distinct lava-currents. A bed of 

 oysters, perfectly identifiable with our common eatable species, 

 no less than twenty feet in thickness, is there seen resting upon 

 a current of basaltic lava ; upon the oyster-bed again is super- 

 imposed a second mass of lava, together with tuff or peperino. 

 Near Galieri, not far from the same locality, a horizontal bed, 

 about a foot and a half in thickness, composed entirely of a 

 common Mediterranean coral (Gary ophy Ilia cespitosa, Lam.), 

 is also seen in the midst of the same series of alternating 

 igneous and aqueous formations. These corals stand erect 

 as they grew, and after being traced for hundreds of yards, are 

 again found at a corresponding height on the opposite side of 

 the valley. 



Dip and direction. The disturbance which the newer 

 Pliocene strata have undergone in Sicily, subsequent to their 

 deposition, differs greatly in different places; in general, 

 however, the beds arc nearly horizontal, and are not often 



