yi Oil the Conslilution of' the Tcniiury of Rome ^ "wHh 



fbunil even in islands and regions quite destitute of fresh waters, 

 or where, at least, they are very scanty ; so Brocchi found it 

 on Ischia and Procida, vvhicli have no rivers ; it has lately heen 

 discovered on Lipari by the researches of the well informed 

 traveller, Mr Ruppel ; and, in Sicily, the tufa is seen in the 

 Val de Noto, where rivers are very scarce. But still more 

 indubitable evidence exists in the numerous organic marine re- 

 mains which the tufa now and then encloses to a considerable 

 height, and of which Brocchi has taken notice in many points. 

 Among others, iherc was found in the Peperino, in a layer 

 of pumice-stone, mixed with granular tufa, 2^ miles from Mon- 

 tallo, on the road from Corneto, many pieces of the shells 

 of the Venus islaiidica. Nearer Rome, at Aqua Traversa, on 

 tlie othei side of Ponte Milvi, shells of sea-mussels occur in beds 

 of tufa, alternating with a loose sand. On the summit of the 

 Monte Cavo, in the Alban Hills, well preserved Bivalve Mu- 

 rines have been dug out of a dark volcanic earth. Sea-bivalves 

 are found near Velletri, in a tufa stratum, which covers a lava 

 stream, some of which are preserved in the museum Borgia, 

 and no less numerous are the examples of such appearances in 

 the Phlegroean fields, on Ischia and in Sicily. 



Since the Italian volcanoes have been raised above the sea, 

 they have no longer formed tufa masses, which can at all be 

 compared with the oldest covering of the volcanic regions. Even 

 the well-known tufa, which envelopes Hercidaneuni, is of very 

 slight cohesion, which it first received by moisture and pressure ; 

 and besides this, Lippi has distinctly shewn it to have arisen 

 from alluvions. Brocchi thinks that, on that account, he may 

 conclude, that the tufa-covering was especially the work of sub- 

 marine volcanoes, or of such whose products were taken and car- 

 ried away by the sea. He rests his opinion upon the known exam- 

 ple of the elevation of an island with an irruption of pumice, 

 mixed with sea-shells, at Santorini, in the Archipelago, to which 

 we might add many which have been observed since. Von Buch, 

 too, considers this view as admissible, from what he says at 

 the conclusion of his treatise on Mount Albano: — " Perhaps 

 Peperino is to be explained as a repeated irruption of ashes, 

 which were much diffused, fell mto the sea, and there assumed 

 a stratified form. With these ashes were ejected, from the in- 



