On the Constitution of the Territwy of Rome, ^e. 97 



a much greater extent. The stream has been once a lake, of 

 whose former existence, indeed, all observers speak, who have 

 noticed this region even in a general way. 



Leopold von Buch, among others, says, — " Every step upon 

 the Roman plain plainly discovers to us traces left by this great 

 lake;" and, in another place, he shews, upon undisputed 

 grounds, that it was just the quiet nature of the deposition, 

 which distinguishes the ancient travertino from what is now 

 deposited in pipes and water-conduits. 



Breislak has, besides, expressly shewn how the formation of 

 travertino, which is still going on under our eyes in the small 

 lagunes of the Solfatara, and in the Lago di Tartaro, at Ti- 

 voli, only presents, upon a smaller scale, the same appearances 

 which once took place in greater magnificence upon the plain of 

 Rome. Yet we cannot forget, that the evidences of a more 

 violent motion of the water of the river, at this period, are in 

 manifest contradiction with these phenomena. They are found- 

 ed on the numerous large boulders of limestone aud basaltic 

 lava which are here and there met with on the travertino, at 

 considerable elevations : for the modern Tiber can no longer 

 roll so far down its bed such masses. Brocchi's observations 

 have shewn, that it deposites its large pebbles at Gavignano and 

 Filacciano, 30 miles from Rome ; and from thence to its mouth 

 only, the well-known yellow fine sand, from which it obtained 

 from the ancients the name of Blonde : — 



" In mare cum^aua prorumpit Tibris aren«." — Ovid. Metam. xiv. 



Leopold von Buch is inclined to seek for this former higher 

 elevation of the fresh waters, in the imperfect retreat of the sea ; 

 and Brieslak, as well as Brocchi, follow him in this supposition. 

 But we neither know whether the present state of things could 

 have terminated suddenly (and perhaps this quick diminishing 

 of the level of the water was the cause of the rolling down of 

 these fragments) ; nor do we know what change this last con- 

 vulsion can have wrought in the constitution of the region. 

 We must admit that we want the knowledge of many consi- 

 derable circumstances in order to explain satisfactorily the nu- 

 merous geological phenomena presented by Rome ; and we may 



OCTOBER DECEMBER 1829- G 



