1850.] MURCHISON—EARLIER VOLCANIC ROCKS OP ITALY. 291 



of which are at some altitude above the river Anio. Charged as it 

 is with fossilized seeds and marsh plants, this travertine was doubtless 

 formed at a period when the waters covered all the lower region of 

 the Campagna, or when very copious mineral springs were in action. 

 It was therefore accumulated when igneous and elevatory action was 

 still acting rifely along all the Italian coast, — that action which had 

 given rise to the earliest volcanic rocks already described, and which, 

 when it had ceased to exhibit its most violent phase, seems to have 

 been followed by a copious evolution of gases and acids, which acting 

 on the limestones of the adjacent Sabine Hills and their outliers that 

 surround this tract, derived therefrom the continuous and rapid addi- 

 tions of old travertine, and saturated therewith very extensive tracts. 

 The small lakes of the Solfatara and Tartaro are now the only re- 

 maining vestiges of the former intense energy which produced the 

 wide-spread masses of old travertine. Explained by Davy and chro- 

 nicled by Lyell, they only acquaint us with the mode of formation on 

 the present minute scale. As no streams or lakes have existed 

 during the historic eera in any portion of the great adjacent low plateau 

 of travertine, with the exception of the pools above mentioned, any 

 more than on the western slopes of the Tivoli Hills, the formation of 

 the enormous breadths of travertine exposed in these localities must be 

 referred to the close of the great subaqueous volcanic epoch which 

 was terminated by the elevation of the Campagna. He who examines 

 the flanks of the Apennines and their recesses, will find, I doubt not, 

 many other masses of travertine equal in extent to those of Tivoli. 

 Such, for example, fell unexpectedly under my own notice as I was 

 returning from Naples by the middle road, where to the north of Feren- 

 tino I saw the apennine limestone and superposed macigno covered 

 on their edges by a great breadth of honeycombed, hard, dry traver- 

 tine, which extended over the broad valley in rough and undulating 

 hillocks occupying many square miles, and surrounded, as near 

 Tivoli, by the volcanic tuff which near Val JMontone fills up all the 

 rest of the trough between the Sabine and Latian Hills, and rises to 

 a considerable height on the flanks of the latter. 



When we contrast these grand operations of ancient nature with 

 the deposits of existhig lakes and rivers, we at once see, that there is 

 the clearest line of separation between them, dependent in fact on 

 great changes in physical geography. Thus, the above-mentioned 

 tract of hilly travertine between the Volscian and Sabine ridges of 

 apennine limestone is separated from all the drainage of the Anio 

 and the Tibur and the Campagna di Roma, by a " divortia aquarum" 

 composed of volcanic tuff. Again, whilst the ancient deposits of 

 Tivoli have taken place where the course of a river, still charged to 

 some extent with lime, may under very diiferent outlines serve to 

 explain the modus opera7idi, here, on the contrary, there is no stream, 

 solfatara, nor lake ; a few pebble rivulets, the feeders of the Gari- 

 gliano, being alone visible at the base of the hills. This travertine 

 tract, then, has also been accumulated towards the close of the 

 earlier volcanic period, and after the tuff of the Campagna had to a 



