1848.] MURCHISON ON THE STRUCTURE OF THE ALPS. 



295 



and Planorbes, based upon and passing into a coarse 

 travertine, with calcareous agglomerate and breccia; 

 4tli, conglomerates of Apennine limestone, the surfaces 

 of the rounded pebbles being often covered with Ba- 

 lani and Serpulse, and associated with yellow sands 

 containing large Ostrese and Pectens, &c. ; these 

 graduate down into calciferous yellow sandstone, the 

 "^«?zcAm«*" building- stone of the country, with con- 

 cretions of calcareous grit, &c. ; 5th, blue marls, which 

 are much richer in shells in their upper parts only, 

 where they graduate into the yellow sands. 



The larger and lower portion of these marls is, in- 

 deed, throughout large tracts as sterile in organic 

 remains as it is in its agricultural character. The 

 desolate region between Siena and Radicofani is en- 

 tirely composed of these naked, dull grey marls. On 

 the other hand, the pebble beds and incoherent sand- 

 stones and marls on which Perugia stands, and in 

 which her ancient Etruscan tombs were excavated, 

 are probably of miocene age. At all events they re- 

 semble the Superga series in mineral aspect, repose 

 upon macigno and alberese, and at Ficullo, between 

 Perugia and Orvieto, are succeeded by unquestionable 

 and very shelly subapennine strata. 



In the volcanic regions extending from Radicofani 

 to Rome, there are no evidences of any stratum older 

 than the blue subapennine marl. To find the equi- 

 valents of miocene deposits in the southern parts of 

 the Papal States, we must either travel eastwards into 

 the valleys of the Apennines, or, passing the axis, ex- 

 plore the rich deposits of that age with plants and 

 shells which await the geologist, who will work out 

 the data of which M. Orsini and Count A. Spada 

 have given a sketch. 



Not intending now to enter upon the consideration 

 of the volcanic dejections of the Papal or Neapohtan 

 States f, I would however say a very few words to show 

 the connection which exists between the subapennine 

 strata that crop out at Rome and their associated 

 rocks, and thus indicate generally the succession of 

 geological pheenomena in the environs of the ancient 



* Although applied to rocks of pliocene age at Siena and 

 Volterra, the term " panchina " is used at Leghorn in reference 

 to a marine tufa or shore deposit, covered by red earth, which 

 is younger, and probably of the same age as the overlying tra- 

 vertines (3) of Siena and Colle. 



t Monsignore Medici Spada and Professor Ponzi prepared 

 and presented to me a map of the volcanic dejections of La- 

 * tiura, which they regard as terrestrial, in contrast with the sub- 

 aqueous formations of the Campagna. They have indeed pub- 

 lished a general section, " Protilo tcoretico dci tcrrcni della 

 Campagna di Roma." 



