Physical Structure of the Site of Rome. 25 



the Apennine valleys. Thus, ascending the bed of the Anio, 

 stony tufa forms lofty nxjks, near Varia, now Vicovaro, above 

 Tivoli, and is met with about 2^ miles from Sublaqueum, now 

 Subiaco. Ascending the valley of the Tiber, it is found sur- 

 rounding the limestone of Soracte on all sides, at Falerii and 

 at Otriculum. In the Campagna, it is found in many places 

 high up on the sides of the hills; likewise on the western 

 side of the Volscian Hills ; and vast deposits of it have been 

 found at Ardea, and about five miles from Rome, on the Via 

 Ostiensis. 



It is an important circumstance to remark, that, on examining 

 minutely the mineral substances of which the tufa found in the 

 Campagna, and between the Volscian mountains and the sea, is 

 composed, there is indubitable proof that they have been derived 

 from the same source as those which form the tufa of the Seven 

 Hills, and not from the adjoining volcanoes of the Alban Hills. 

 The tufa in the valley above Tibur is identical with that of the 

 Tarpeian Rock*. 



The volcanic products are, in their turn, covered with fresh- 

 water deposits, for these have been found in a great variety of 

 places throughout this district : indeed, all the way from Vulsinii 

 to PiEStum. 



The facts here narrated evidently point out that this country 

 has undergone great changes, — that these changes must have 

 occurred at distant epochs, — and that, during the intervals of 

 the later changes, there probably existed the same repose in the 

 greater operations of nature, as we know to have prevailed since 

 the earliest records of history ; for although the neighbouring 

 Campi Phlegraei have been repeatedly disturbed by volcanic ac- 

 tion, Latium, and the whole region north of the Liris, is the 

 same now as it ever has been since it was possessed by the hu- 

 man race (as far, at least, as we have any means of knowing or 



• Hot springs, emanations of gas, sulphurous vapours, and sublimations of 

 sulphur, are of common occurrence. Between Home and Tibur, in the Lo- 

 cw AlbiUtty now called Solfatara and Lago de Zelfo, the water is tepid, 

 is saturated with carbonic acid gas, and holds a vast quantity of lime in 

 solution. " The stream which flows out of this lake fills a canal about nine 

 feet broad and four deep, and is conspicuous in the landscape, by a line of 

 vapour which rises from it." — Lyell, 207- 



