214 
FOREIGN EQUIVALENTS. 
by Prof. Sacco, this area may be taken as showing the character 
of the deposits in northern Italy. In his latest publications 
Prof. Sacco divides the Pliocene series thus* :— 
Metees, 
Possanian (Fosaanimo) 
_ ^ l. or estuarine - - - 
Astian (Astiano) - Marine sands, with, beds of Oysters 
Plaisan«ian(Piaceiitmo){““'g®y^"<l.‘’l''y®’ 5“'^ of^ marine 
r Sandy marls, sometimes clayey, with 
Messinian J seams of gypsum, limestone, and marine 
(Messiniano). | fossils. Alternating brackish-water and 
L marine ----- 
There is a gradual passage between each of the divisions, and 
the lowest, the Messinian, rests conformably on, and passes down 
into the Tortonian (Miocene). 
A like succession has been made out in Liguria by C. Mayer, 
and a similar series of changes, from the brackish-water Messinian 
to the deep-water Plaisancian, then to shoal-water Astian, 
becoming littoral at the top and passing into freshwater deposits 
variously named Arnusian, Villafrancian, &c., seems to have 
taken place throughout great part of Italy. In Sicily the 
Messinian division, or Zanclean ” as it was named by Prof. 
Seguenza, has apparently become more marine, though great part 
of it is unfossiliferous. Until, however, the detailed work of the 
Italian Geological Survey is more advanced, a good deal of the 
correlation of the minor divisions must be treated as provisional, 
for the mass of the deposits is great, and their thickness 
and lithological character vary considerably according to the 
proximity to the Apennines. In Tuscany there is still great 
uncertainty as to the exact relations of the celebrated lacustrine 
deposits of the Upper Val dArno with the marine Sub-Apennine 
Strata, only a few miles away. This will be again alluded to 
further on. 
The lowest of the stages of the Italian Pliocene contains a 
molluscan fauna so unlike that of the Mediterranean, and having 
so large a proportion of extinct species—about 83 per cent.— 
that, as already observed, it is evidently older than any Pliocene 
deposit found in England. It probably represents the interval 
between the Bolderian and Diestian formations of Belgium. 
From one third to nearly half the Plaisancian mollusca belong 
to living forms. There is a gradual change upwards, and a 
nearer approach to the existing fauna of the Mediterranean, till 
in Sicily we reach a stage, higher than the Astian, named 
‘‘ Sicilian ” by Prof. Seguenza. This latest stage contains a 
fauna scarcely differing from that now found in the adjoining 
seas, except that among the fossils are a few northern forms, 
See Bull. Soc. Beige de Geologic^ vol. iii., pp. 12-28. (1889), &c. 
