File:The Quarterly journal of the Geological Society of London (12645302693).jpg

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