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



in the form of subaqueous detritus. This supposition is, indeed, fully 

 confirmed by all the accompanying phsenomena in the Campagna 

 around Rome, where skeletons of elephants, rhinoceros, deer, and 

 other quadrupeds are not only found in the subapenniue marine 

 strata, but also in the subsequently formed igneous rocks and tra- 

 vertines ; and to none of these deposits has any other origin been 

 assigned, than that of accumulation under water, whether salt, 

 brackish, or fresh. When I examined the grand and deep quarries 

 of peperino near IMarino, and between that place and Albano, and 

 saw their amorphous and solid character, I had no doubt that they 

 were of anterior date to the higher and central scoriaceous erup- 

 tions of Monte Cavi, which, as I have stated, alternate with and 

 overlie peperino. If this peperino had been emitted as a lateral 

 outburst of hot mud whilst the central volcano of Hannibal's 

 Camp was active, and had flowed upon ground which had then 

 assumed its present form and terrestrial conditions, surely we should 

 see in it something like a lava formed under the atmosphere, and its 

 surface, if not rugged, would, at all events, be more or less porous 

 and scoriaceous, and not the hard, compact building- stone which it 

 is. I could see no sort of evidence to prove that the peperino of 

 Marino was of a different age from that of Albano ; on the contrary, 

 I believe that they are integral parts of one and the same subaqueous 

 matter, ejected under pressure around the roots of a group, whose 

 central cone and crater were rising into the atmosphere. 



If then we are to admit, that there is any true analogy between 

 Hannibal's Camp and authenticated subaerial volcanos, we must 

 allow, that the most modern dejections are those which proceeded 

 from the higher crater, whilst most of the great amorphous lateral 

 masses may very well be referred to an anterior period, and to fonna- 

 tions accumulated under other conditions. 



In viewing the Latian Hills as a whole, I should therefore say, that 

 their flanking cavities, still filled with water, whether cup-shaped like 

 Nemi, or elliptical like Albano, are to a great extent analogous to 

 those of Baccano and Bolsena, north of Rome. I believe that, to- 

 gether with the igneous rocks which form their banks, they were 

 accimiulated under more or less aqueous pressure, and never were 

 true subaerial volcanic vents ; though they probably were apertures 

 produced by the explosion of heat and gases when all the volcanic 

 materials were under water. On the other hand, the true crateriform 

 depressions of Hannibal's Camp and its parasites were, as I think, 

 the lofty spiracles by which the volcanicity was let off, — viz. when 

 the gromids were emerging, or had partially emerged from the sea, 

 and were attaining their present outlines. The probable result of 

 this last operation in the series of elevations and eruptions might be, 

 that by the rising up of the central volcano the surrounding and pre- 

 existing masses would radiate from it and slope down into what is 

 now the adjacent low country, as they now do, and thus be in this 

 sense a crater of elevation. I may further observe, that on inspect- 

 ing this system of hills I was impressed with the idea, that, whilst 

 its uppermost dejections bore some resemblance to the extinct volca- 



