322 THE ROMAN CAMPAGNA 



dynamite. Passing through this busy scene, he soon 

 perceives that the ancient bank against which the 

 Tiber chafed when it was spreading out its high 

 alluvial plain, has been quarried backward, and as the 

 ground slopes upward from the plain, the cliff thus 

 artificially cut open must be continually changing its 

 face and becoming higher. At present there has been 

 laid open an excellent section of strata forming part 

 of the upper or sandy group of Monte Mario. These 

 succeed each other in horizontal bands so diverse in 

 form and colour as to give the cliff a markedly banded 

 aspect. 



At the southern end of this section some layers of 

 coarse gravel may be seen cemented into a solid cal- 

 careous conglomerate full of large and well-preserved 

 marine shells. A little further over comes a band of 

 travertine — a compact variety of limestone which is 

 one of the characteristic and economically important 

 stones of the Campagna, for where of good quality, 

 it makes an admirable firm cream-coloured building- 

 stone, which has been largely used from the early times 

 of Roman history. To its durability the preservation 

 of so many noble monuments of Republican and 

 Imperial architecture is due. I may remark in pass- 

 ing that this material can now be seen in actual 

 course of deposition from solution in the neighbour- 

 hood of Rome. The cold waters of the Anio have 

 formed thick masses of it at the Tivoli Falls, and the 

 warm springs of Bagni deposit it on the plain below. 

 At the latter place its accumulation must have been 

 going on for a vast period of time, seeing that it 

 now covers a tract of the low ground to the north 



