Observations on the Geognostic Character of Italy. 87 



ot'theEsquiline, of the Viminal, and Quiriiial : its relations are, however, most 

 striking on the Pincius. We there see, at the cluirch of tlie Augustines, close 

 to the Porta del Popolo, a thick bed of granular tufa projecting out, in which 

 are masses of cellular travertine, with impressions of reed-like vegetables, 

 and also leaves of the Populus alba, Betula alnits, and small twigs of the 7*0- 

 marix galliea ; there was also found here the fragment of an unknown bone. 

 Over it lies a grey fluviatile clay, with impressions of leaves of the Sali^ 

 alba, and then come those numerous alterations of volcanic tufis, fluviatile 

 sand, and more or less complete strata of travertino, to a height of more than 

 130 feet above the level of the river. Leopold von Buch first observed that 

 this was constantly the relation of the travertino to the strata of tutt' in this 

 part of Rome, and he has completely deinonstrated, that the Pincio forms, 

 in a certain measure, the commencement of a considerable ridge of preci- 

 pitous travertino rocks, which, on the outside of Rome, are continued unin- 

 terruptedly from the Porta del Popolo to Ponte Molle, and in which this 

 order of superposition often recurs. In this rocky ridge are the catacombs of 

 St Valentino, in the vineyard of the Augustines at Papa Giulio, the only ones 

 in the environs of Rome which do not occur in a volcanic rock. Near this 

 spot Leopold von Buch mentions the occurrence in the travertino of distinct 

 impressions of the leaves of the plane tree, chesnut, nut-tree, and laurel. 



We shall reserve for the following section what explanations are to be 

 sought of these important relations. Yet here it merits observation, that 

 even on the right bank of the Tiber, the travertino formation is by no 

 means of rare occurrence. We have already seen that it exists outside Rome, 

 at the Torre di Quinto. Leopold von Buch has given a remarkable locality 

 at the chapel of St Andreo. But within the walls of the city are seen many 

 cellular concretions of calc-tufF in the fluviatile sand on the declivity of the 

 Janiculus ; and Breislak and Leopold von Buch there found, under the walls 

 of the Villa Pamfili, in the granular tufa itself, a piece of travertino enclo- 

 sed, in which were found well-marked Helicitei. 



B. Conclusions from the Geognostic appearances of the Roman 

 Territory. 



In the foregoing exposition of" the facts, which an attention 

 to the constitution of the Roman soil ])i-esents to the intelligent 

 observer, it was our intention, as much as possible, to limit our- 

 selves to the space included within the walls of the city. The 

 wish to explain the appearances, and, as much as possible, to 

 connect them with the relations of this territory, necessitates us 

 to leave these limited bounds, and to give a glance at the struc- 

 ture of the Italian Peninsula. 



Italy, traversed with sliglit ttxccptions, throughout its whoic 

 length by the gigantic ridgo of the Appenincs, is naturallv 

 divided into two nearly equal iialves, but of essentially different 



