16 Account of the . 



The Aventine Hill is the lowest of all, being only 133 feet 

 al)ove the river. Under this name, however, are comprehended 

 two distinct eminences, separated by a valley or mtermontium. 

 It was that part next the river which alone received in former 

 times the name of the Aventine Hill. It is chiefly composed of 

 stony and granular tufa, the latter containing many indications 

 of recomposition ; but, on the side which overhangs the Tiber, 

 there are extensive deposits of sand and marl, together with 

 thick solid horizontal beds of travertino, extending above half 

 a mile. This travertino contains numerous fresh water and 

 land shells, among which are found the shells of snails now com- 

 mon in the gardens of Rome. It also contains fragments of 

 pumice. 



I shall now proceed to describe the hills on the right bank of 

 the Tiber, which differ very materially from those on the left 

 bank, as they are mainly composed of marine strata. There 

 are three marked eminences, the Janiculum, the Vatican, which 

 is a continuation of the Janiculum, and Monte Mario, which is 

 a continuation of the Vatican Hill ; the three forming one ridge, 

 interrupted only by slight depressions and valleys. 



Monte Mario. — This hill rises to the height of 446 feet above 

 the Tiber. It is composed of sand, in some places wholly sili- 

 ceous, in others siliceo-calcareous, containing in several situa- 

 tions thin beds of gravel and masses of solid sandstone, and full 

 of marine shells. Large oyster shells have been found in abun- 

 dance on the very summit., as well as marine shells of other spe- 

 cies and genera. Univalve and bivalve shells are also seen ad- 

 hering to the pebbles or the beds of gravel, evidently shewing 

 that these pebbles once lay at the bottom of the sea. This sili- 

 ceo-calcareous sand is of the same nature as that which forms 

 the chief parr of the low sub-appenine hills throughout the 

 whole of Italy. It is in general loose, and without aggregation; 

 but, in some places, it is agglutinated with a pretty solid stone. 

 Under this bed of sand lies a bluish clay, regularly stratified, 

 full of marine shells. 



The Vatican is a low hill, being not more than seventy-eight 

 feet above the river. In composition it is similar to that of 

 the Monte Mario. The clay found in this hill is used now to 



