300 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 6, 



which occurs at Porto d'Anzo*, imhodies fragments of rocks de- 

 rived from what I have shown to be the newest portion of the Latian 

 volcanos, and in addition to leu cite contains crystals of pyroxene and 

 peridote ; minerals which first made their appearance in the Tolcanic 

 products of that time, and have not been detected in the more ancient 

 tufaceous and igneous rocks of the Campagna. Now, Porto d'Anzo 

 or Antium is about twenty-fiye miles distant from Hannibal's Camp, 

 and as a volcano of its small size could not be expected to eject solid 

 contents to a distance far beyond that to which Yesu'S'ius now occasion- 

 ally projects fragments in showers, so we have a right to infer, that 

 when the Latian volcano was in activity, the sea approached very near 

 to i^s periphery or roots. In this case we should have no difficulty in 

 accounting for the washing away of its materials to the spot where 

 Porto d'Anzo now stands, there to form part of the Mediterranean 

 deposits which were afterwards to be elevated, constituting the raised 

 beaches of " Macco." In like manner I would explain the transport 

 of the huge blocks of the Latian volcanic rocks to the neighbourhood 

 of Rome before adverted to. At all events the facts at Porto d'Anzo 

 are sufficient to prove that the relations of land and water have un- 

 dergone very great change since the activity of the youngest of the 

 Latian volcanos ; and it appears to prevent our extending true ter- 

 restrial volcanicity beyond the limited area in this region to which I 

 have attempted to restrict it f . 



Rocca 'Monfina. — I now beg to say a few words upon that remark- 

 able volcanic tract, called Rocca ]Monfina, in the kingdom of Naples, 

 which has been described by several foreign authors J, to which Dr. 



* On the authority of Professor Podzi. The quaternary of some Italian geo- 

 logists is supposed to have been formed since the habitation of the peninsula by 

 man, but this point is not well estabUshed. 



t After these pages ■were written, I learnt that Professor James Forbes had read 

 a memoir on the Latian volcanos before the Royal Society of Edinburgh, on the 

 29th January 1850, On communicating with him, 1 find that he differs from me 

 as to the origin of the Lake of Albano and its peperino, and agrees, as far as I un- 

 derstand, in the main with the \-iews of Spada and Ponzi. As Prof. Forbes has paid 

 more attention than myself to the mineral structure of the Alban rocks, my readers 

 must necessarily consiilt his forthcoming memoir, of which I have only seen the 

 abstract. He thinks that the land was already covered with vegetation when tre- 

 mendous outbursts forced open the cup-shaped cavities of Albano and Nemi, and 

 that mud eruptions from lateral orifices were poured forth since the gi'oimd assumed 

 its present relations and outline (as at Marino). He seems to bebeve in three pe- 

 riods of peperino and lava dejections, all subaerial. To these views I cannot sub- 

 scribe, for the reasons adduced in the text. I cannot imagine that the deep lake 

 depressions of Albano and Nemi, with their solid lofty cliffs and unbroken sides, 

 were ever subaerial volcanos. Nothing like these, I would suggest, has ever been 

 formed by volcanos in modern ages : nor do I comprehend how the enormous 

 thick masses of peperino which are opened out in the quanies of iMarino, should 

 have issued from the extreme, external, and lower flank of a volcanic group, which, 

 according to the admission of Spada, Ponzi, and Forbes, must have had (and 

 probably, as they say, at the very same time) an unchecked orifice in the great 

 central crater of Hannibal's Camp. I repeat, that it is with diffidence that I op- 

 pose this portion of the ^iew of these my friends and contemporaries, but, with 

 my present knowledge, I adhere to the line T have adopted. In considering the 

 chief Latian volcano subaerial we are all agreed. 



X See BreislaJc, Voy. Phys. et Lithol. dans la Campanie, 1801 ; Abich, Ueber 



