202 TRAVELS THROUGH 



mon road to the villa Mellim, and villa Madama, 

 on wcnle^MariO) fince it is deeply cut into this 

 hill, which in greater depth may probably contain 

 many more fuch marine ftrata. 



This defcription of monte Mario, and of other 

 like hills, ieems to fupport the inference, that they 

 have been immediately depofited by the fea, and 

 that the inclofed ofteocolla-lumps have been pro- 

 duced by the foaking and filtering of waters. The 

 compact limeftones in the Apennines are feparated 

 from thefe hills by the valley between Rome and 

 Tivoli, which is covered by volcanic allies. Hence 

 \ve may conclude, with fome probability, that the 

 Apcnnine limeftone beds are continuing under the 

 volcanic productions of the valley towards the 

 Roman calcareous hills * which, on this account, 

 are in the fame proportion to the Apennines, as 

 the Viccntine colls s teriiarii are to their monies fecun- 

 darii. The volcanos therefore have forced here 

 their way through the inferior limeftone, and fpread 

 their a&es over the lower calcareous plains, leaving 

 the higher hills uncovered and bare. This opinion 

 is ftrongly countenanced by the frequent limeftone- 

 fragments in the Piperinos, lavas, and yellow- 

 Lro-wnifo tufcs, by their effervefcence with the acids, 

 ancl by the loofe feparated ft ray ing limeftones on 

 monte Allans. The volcanic productions have been 

 afterward covered in ma y places, as near Tivolt^ 



with 



