1850.] MURCHISON— EARLIER VOLCANIC ROCKS OF ITALY. 29.5 



centre in the form of great bands. Long, however, before I reached 

 the ascent to Albano or Frascati, occasional and isolated blocks of a 

 very different sort of lava were pointed out to me by Ponzi. These 

 contain crystals of pyroxene, and he supposes that they have been 

 hurled from a quondam volcanic orifice in the Latian Hills (such as 

 the Camp of Hannibal, to which I shall hereafter specially advert), 

 and projected to their present habitats in the Campagna distant ten 

 miles from the supposed source of their origin. I shall, however, 

 endeavour to account for the dispersion of these materials in another 

 manner, before I close my description of these Latian volcanos. 



In ascending from the Campagna to Castel Gandolfo and the Lake 

 of Albano, immense sloping mounds of grey peperino, fig. 3, 3, & fig. 

 4, 3, 3, are exhibited, in which, in addition to numerous crystals of 

 leucite and occasionally other simple minerals, there are large angular 

 fragments of Apennine limestone, some of which are in a highly altered 

 state, and also portions of pre-existing crystalline rocks, containing 

 mica, pyroxene, garnets, and Hauyne. I confess that I could not see 

 any great geological distinction between the compact leucitic peperino, 

 which occupies the high point on which the convent of the Cappuccini 

 stands, as well as the cliffs around the beautiful, deep, oval-shaped 

 Lake of Albano, and the leucitic rocks of Bolsena and Acquapen- 

 dente before described ; nor can I believe that there was any great 

 difference in their age or in their method of emission. For here, 

 as in the so-called parasitic crater-lakes north of Rome, the high 

 walls or banks of the Lake of Albano are completely unbroken, 

 without the semblance of any gap or opening by which a coulee 

 of lava could have flowed. It is true, that about a mile to the south 

 of Albano, and nearly on the same level as that town, a new cut in 

 the road, made in establishing a bridge, has exposed grey leucite 

 lava, overlying unconformably the ordinary reddish tuff of the 

 Campagna ; but half a mile further on, at Lariccia, these two rocks 

 are conformably arranged, and the same system and relations con- 

 tinue to Velletri and Cisterna. Now if the red tuff, which is admitted 

 to have been a subaqueous deposit, had been elevated into land before 

 the peperino and grey lava flowed upon it, surely we might expect to 

 see some trace of a terrestrial surface, some dirt-bed with remains 

 of vegetable substances between the tv/o rocks ; but such is not the 

 case, and the one is at once incumbent on the other. 



In mounting from the outer portion of the circle, or from the 

 level of the rocks which encompass the Lake of Albano to Rocca 

 Papa and Monte Cavi (the culminating point of this cluster of hills, 

 on which the Temple of Jupiter Latialis stood), it seemed to me, 

 that near a little chapel the upper courses of the peperino, or out- 

 ward fringe of rocks, alternate with, and are finally overlapped by, 

 layers of scoriae and lapilli of a brownish red colour'''. Still higher 



* Though I came to the conclusion that the scoriaceous lava overlaid the pe- 

 perino, I beg that my cursory researches may be well tested before they are al- 

 lowed to prevail against the inferences drawn by local observers. I gather, indeed, 

 that Hoffmann viewed the succession in somewhat the same light as myself; 

 for, although he enters into no details, he explicitly states, that the isolated 



