1850.] MURCHISON — EARLIER VOLCANIC ROCKS OF ITALY. 293 



during a high flood in 1826 a great calamity occurred. Having risen 

 suddenly to some height above its maximum level, the water, unable 

 to escape, was thrown back so violently against the south-eastern 

 corner of the town above the bridge, that it broke away the travertine 

 cliffs, and with their fall demolished the church of S*^ Lucia and 

 thirty-six houses, nearly all the transportable materials of which were 

 hurled down torrentially through the cataracts and falls. In this 

 transport it happened, that some of the largest beams of the church 

 stuck fast in the grotto of the Syren, and one of them in particular still 

 remains like a bone in the gullet of an animal, and will doubtless in 

 due time get buried in travertine, which though formed only a few 

 years ago, is apparently subjacent to a great mass of rock, accumulated, 

 I have no doubt, before the Roman sera. As in future ages this 

 beam of a church (and many other materials) may be found lodged 

 or deposited apparently in the body of the travertine, it might 

 be inferred (particularly as the course of the Anio has now been 

 greatly changed) that the church rafters were contemporaneous with 

 the formation of the ancient travertine. In like manner I believe 

 that the cart-wheel alluded to by Sir C. Lyell may have been trans- 

 ported at a comparatively recent date, and was by some such opera- 

 tion wedged into a recess of the older rock. 



In truth, the travertine formed only a few years ago cannot easily 

 be distinguished, if at all, from that of the post-pliocene period. 

 Agreeing therefore with Sir C. Lyell, that the greater portion of this 

 calcareous formation was accumulated in lakes, which he admits may 

 have been for the most part anterior to the sera of history, I differ 

 from his inference, that any portion of the lake, in which the old 

 travertine on which Tivoli stands was accumulated, could have been 

 un drained when the cart-wheel in question was deposited. The 

 natural sections which expose the edges of the strata of volcanic tuff, 

 covered by great bands of travertine, in the cliffs far above the Cam - 

 pagna di Roma (see fig. 2, p. 290), must convince us that the physical 

 outline of the region was very different from that which now prevails, 

 when such travertine could have been accumulated in a lake of which 

 we nowhere see the western barriers*. 



There can then be little doubt, that all the earlier volcanic 

 rocks of the Campagna di Roma, and the great travertines which 

 accompanied or followed their evolution, were formed under sub- 

 aqueous conditions. The marine animals of the former sea were 

 associated with and succeeded by spoils of terrestrial life washed 



* The noble and spirited work executed in the Pontificate of Gregory XVI,, to 

 prevent all such catastrophes as that of 1826, gives a straight and direct issue to 

 the great body of the Anio, by a magnificent tunnel cut right through the pro- 

 montory of apennine limestone, called Monte Catillo, which has for so many ages 

 thrown off the waters upon the travertine plateau of Tivoli. Though a capital 

 piece of engineering and highly useful, this work will however assuredly fall under 

 the anathema of all lovers of the picturesque, who never can endure the comparison 

 of the present straight and smooth fall of the chief mass of water with the old upper 

 falls, the beauty of which is now to a great extent destroyed by the loss of two- 

 thirds of the water which formerly rushed down them. Still the grottoes are well- 

 worthy of being visited. 



