M. Brongniart on the Fresh-water Formations of Italy, 97 
The coarse sandstone formation, composed at its lower 
part of bluish argillaceous marl, with shells, and towards its up- 
per part of reddish sandy limestone, and sometimes of marine 
sandstone, as it occurs in perfection in Rome, at the foot of the 
Monte-della- Grit a, a small hill parallel to the Janiculus, and 
which is itself a detached part of the same hill. 
3d, The volcanic breccia, in all its modifications, lying above 
this formation, as it is very distinctly seen at Mount Marius. 
4>th, Lastly, The fresh-water formation. It would, there- 
fore, be here in a different position from that which I have ex- 
amined in Cantal, in the department of the Puy-de-Dome, and 
in that of Allier. These might be referred to the middle or 
gypseous fresh-water formations, and those of the Roman states 
to the fresh-water formations superior and posterior to the 
second marine formation ; and this relation still agrees perfectly 
well with the position which M. Prevost has assigned to the 
coarse limestone formations of the Apennines. 
I have said, that there are also pretty considerable formations 
of fresh-water limestone or travertine, on the side of Civita 
Vecchia. We begin to see it forming large flats, near Mala 
Grotta, and at Suido. It ceases afterwards, but after ha- 
ving passed the Pulidoro, and the hamlet of this name, we tra- 
verse considerable masses of fresh-water limestone, which form 
projecting, and as it were protuberant parts, which have the ap- 
pearance of being advanced toward the sea in the manner of a 
bed of lava. It is at Monterone that it is most abundant, and 
in the greatest masses. It rests here upon a rock which pos- 
sesses all the characters of the transition formation. 
The celebrated falls or cascades of Tivoli are not owing to 
cliffs of the compact limestone, which forms the mass of these 
mountains, but to a damming (banage) of the valley, produced 
by depositions from the waters which flow through it, and which 
had, in earlier times, been more impregnated with calcareous 
matter, than they are at the present day. This agitation of the 
waters gives to the deposit undulations, which it is not seen to 
have in the plain, and the less abundant precipitation permits 
the limestone to assume a crystalline texture and aspect, which 
gives it more of the nature of alabaster than of travertine. This 
same disposition, dependent upon the same causes, is observed 
VOL. VIII. NO. 15. JAN. 1828. G 
