204 
ELEMENTS OE GEOLOGY. 
Fior. 132. 
shell had not died out in the era of the Red Crag by the dis¬ 
covery of the same fossil near Southwold, in beds of the later 
Norwich Crag. 
Antwerp Crag.—Strata of the same age as the Red and 
Coralline Crag of Suifolk have been long known in the coun¬ 
try round Antwerp, and on the banks of the Scheldt, below 
that city; and the lowest division, or Black Crag, there 
found, is shown by the shells to be somewhat more ancient 
than any of our British series, and probably forms the first 
links of a downward passage from the strata of the Pliocene 
to those of the Upper Miocene period. 
Newer Pliocene Strata of Sicily. —At several points north 
of Catania, on the eastern sea-coast of Sicily—as at Aci-Cas- 
tello, for example, Trezza, and Nizzeti—marine strata, asso¬ 
ciated with volcanic tuffs and basaltic lavas, are seen, which 
belong to a period when the fi rst igneous eruptions of Mount 
Etna were taking place in a shallow bay of the Mediterra- 
• nean. They contain numerous fossil shells, and 
out of 142 species that have been collected all 
but eleven are identical with species now liv¬ 
ing. Some few of these eleven shells may pos¬ 
sibly still linger in the depths of the Mediterra¬ 
nean, like Murex vaginatus^ see Fig. 132. The 
last-mentioned shell had already become rare 
when the associated marine and volcanic strata 
above alluded to were formed. On the whole, 
the modern character of the testaceous fauna 
under consideration is expressed not only by 
the small proportion of extinct species, but by 
the relative number of individuals by which 
most of the other species are represented, for 
the proportion agrees with that observed in the present fauna 
of the Mediterranean. The rarity of individuals in the ex¬ 
tinct species is such as to imply that they were already on 
the point of dying out, having flourished chiefly in the earlier 
Pliocene times, when the Subapennine strata were in prog¬ 
ress. 
Yet since the accumulation of these Newer Pliocene sands 
and clays, the whole cone of Etna, 11,000 feet in height and 
about 90 miles in circumference at its base, has been slowly 
built up; an operation requiring many tens of thousands of 
years for its accomplishment, and to estimate the magnitude 
of which it is necessary to study in detail the internal struc¬ 
ture o^the mountain, and to see the proofs of its double axis, 
or the evidence of the lavas of the present great centre of 
eruption having gradually overwhelmed and enveloped a 
Murex vagina- 
tus, Phil. 
