Observations un the Geognostk Character of Italy. 95 



terior, the basalts and limestones which are now enveloped in 

 the Peperino." 



The same is expressed by this naturalist, when, in another 

 place, he observes, on the great extent of the pumice of the 

 Vatican as far as the vicinity of Civita Vecchia : — " But what 

 other agent than an universal water, without any violent agita- 

 tions, could have extended these horizontal strata over such a 

 space ?" 



But to what is owing the singular reciprocal mixture of tra- 

 vertine and tufa strata, which we have mentioned above ? Broc- 

 chi has explained himself on the point, and, as we think, satis- 

 factorily. He esteems it probable, that all the tufas, which 

 either rest on travertino, or contain fresh-water products, are 

 no longer in their original condition. They must have been de- 

 posited in their first position by the same waters, which brought 

 together the constituents of the travertino, and have subse- 

 quently been united by the chemical operation of the dissolved 

 substances. 



We must, therefore, according to Brocchi, distinguish the 

 Tufa or'tginale and tricomposto, since both are extremely simi- 

 lar in their external characters, and can only be separated by 

 the relations of their position. Yet we must observe, what is of 

 undoubted interest for the history of the Roman territory, that 

 even, according to Brocchi's very industrious researches, the 

 matrix of the Roman tufa has not, as might be at first ima- 

 gined, been in the Alban Hills. It must rather be sought, with 

 more probability, in the more distant Monti Chnini, and in 

 the hills round the Lago di Bracciano. On this he has often 

 observed, in his Catalogo Racionato, that the present existence 

 of pumice-stone, in the tufas at Rome, is evidently at variance 

 widi their origin from the hills of Albano and Tusculum. 

 These volcanoes, as Gmelin has already observed, have never pro- 

 duced any pumice ; and we do not find in them the Roman lithoi- 

 dal tufa, but constantly the peperino, which is foreign to Rome. 

 According to the opposite authorities, a lithoid tufa extended 

 itself from Rome, of which the Roman is only a slight variety, 

 to far beyond the hills of Cin)ini. It is reddish brown, or red- 

 dish yellow, contains felspar, and large pieces of orange-colour- 



