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



up, and reaching Rocca Papa, all traces of the peperino vanish, and 

 from thence to the summit of Monte Cavi, about 3100 feet above 

 the sea, the whole mass consists of a portion of that grand scoriaceous 

 and cindery accumulation which forms the circumference of the de- 

 pression called Hannibal's Camp, fig. 3, 4, and 4, 4, 4. Very different, 

 indeed, from that peperino, which I consider to be subjacent (or 

 formed under different conditions), are those scoriaceous dejections 

 which have, to a great extent, a terrestrial or atmospheric aspect. 

 Here also, in physical outlines, Ave reach something like an analogy 

 to the phsenomena of Auvergne ; for w^e see that one of the faces of 

 the brim which encircles the depression in which Hannibal encamped 

 (^. e. to the north-west) is broken down, as expressed in a map of the 

 tract prepared for my use by Professor Ponzi (fig. 3, p. 284). Again, 

 all the rocks surrounding this semicircular cavity bear signs of sub- 

 aerial volcanicity. Scoriaceous fragments and loose lapilli are arranged 

 in fine laminae, unlike the great amorphous masses of the Alban pepe- 

 rino, and they are associated with what much resembles portions of 

 coulees of lava. I further observed tortuous, rope-shaped coils of 

 scoriae, like those which so abound at Vesuvius, and spherical and 

 flattened geodes of the same substances. Again, these volcanic dejec- 

 tions are traversed by dikes like those of Somma, the modern ana- 

 logues to which are even seen in Vesuvius. When, however, we come 

 to judge from the mineral characters of all the associated rocks, there 

 are difficulties in identifying some of them with known subaerial pro- 

 ductions. Thus, there are apparently issues of matter which the 

 Italian geologists call tephrine lava, containing calc spar, Gismondine, 

 and pyroxene, and which, but for the difference of the imbedded 

 simple minerals, pointed out to me by Spada, I could not distinguish 

 from those basalts of Radicofani and Acquapendente which were 

 unquestionably formed under the waters. There is also a greenish 

 leucitic rock with crystals of dark pyroxene, together with some 

 olivine. Again, there is a very peculiar lava in these dikes and coulees 

 in the form of a roughish, light, and somewhat porous trachytic rock, 

 called *Asprone' by the country people ('Sperone' of authors), 

 which near Rocca Papa is copiously charged with small garnets. It 

 is this 'Asprone' which is largely quarried as a building-stone in the 

 adjacent hills of Tusculum. 



In respect to the general relations of Hannibal's Camp, it must be 

 admitted, that as all the scoriaceous accumulations occupy hills from 

 500 to 700 feet higher than the valley they encircle, and as their 

 strata dip away from it, and also have a broken-down orifice on the 

 north-west, the whole scene, as well as the lithological aspect of the 

 rocks, leads to the belief that this may have been a subaerial volcano. 

 At the same time, if such it has been, the volcanic action must have 

 been of very remote antiquity. In proof of this, the sandy and 



mountain, of which Monte Cavi is the highest point, is " probably the only crater 

 in the Papal States from which a perfect volcano or volcanic cone, like that of 

 Vesuvius, still rises up, v^hich has been active since its emergence from the sea." 

 (See Geognostische Beobachtungen durch Itahen und Sicilien, von F. Hoffmann. 

 BerUn, 1839, pp. 47, 48.) 



