260 



which, on the authority of Ponzi, appear to have ejected peperino. 

 'ihe horse-shoe form of the old crater of the Alban Mount, which, 

 whether formed by the elevation process or not, appears to be com- 

 posed of beds of basalt, lapilli, tufF, or peperino, and here and there 

 of the lava called Sperone, gave way, like that of Somma, on the 

 western or seaward side, and I cannot but think it in no small de- 

 gree probable, that the vast lava beds which lie under Nemi and 

 Genzano, and which dip at a small angle under Monte Cavo, are 

 part of the dislocated walls of the ancient crater displaced by the 

 convulsion which rent it on the western side, and which was accom- 

 panied by a prodigious fluid discharge of peperino, which then 

 formed the strata of La Riccia and Albano, and which, overwhelm- 

 ing the broken-down wall of the ancient crater, formed at the same 

 time the Monte Gentile, and the peperino beds above Nemi. This 

 is confirmed by the prodigious lava blocks imbedded in these rocks, 

 which bespeak the violence of the convulsion during which they were 

 formed. Acres later, the present summit of Monte Cavo and the crater 

 of the Campo d'Annibale were formed, and the latter gave out its cur- 

 rents of tefrine or grey basalt, and raised the crater of La Tartaruga 

 and others in the valley of La Molara, and in the central crater; at the 

 same time ejecting great volumes of pulverulent lapilli. It may have 

 been coeval with these perfectly regular and comparatively modern 

 eruptions, or it may have preceded them, that, after a period so long 

 that the surface of the ancient eruptions of peperino were covered 

 with vegetation and timber, the ti'emendous outbursts which forced 

 open the craters of Albano and Nemi took place, the former pro- 

 ducing some slight ejections of peperino or boiling mud, near Castel 

 Gaudolfo ; and at the same time a separate orifice, opening at the foot 

 of Monte Cavo, may have discharged into the valley of Marino the 

 remarkable variety of peperino described in this paper, and containing 

 vegetable stems. A long, perhaps even a final, repose succeeded this 

 paroxysm. Even from the very dawn of Italian history these scenes 

 of previous turmoil and desolation appear to have enjoyed profound 

 tranquillity, and to have been immemorially covered with impenetra- 

 ble groves sacred to the sports of Diana. 



" It will be seen, then, that we admit tufas or peperinos of three 

 very different periods, one of which is coeval with, or even anterior to, 

 the formation of the exterior cone, another largely developed, which 



