Ch. XII.] ORGANIC REMAINS OF SUB APENNINES, 163 
these pushed their deltas farther out, they threw down the 
sand upon part of the bed of the sea already occupied by finer 
and more transportable mud. 
Organic Remains. — I have been informed, by experienced 
collectors of the Subapennine fossils, that they invariably pro- 
cure the greatest number in those winters when the rains are 
most abundant, an annual crop, as it were, being washed out of 
the soil to replace those which the action of moisture, frost, 
and the rays of the sun, soon reduce to dust upon the surface. 
The shells in general are soft when first taken from the marl, 
but they become hard when dried. The superficial enamel 
is often well preserved, and many shells retain their pearly 
lustre, and even part of their external colour, and the ligament 
which unites the valves. No shells are more usually perfect 
than the microscopic, which abound near Sienna, where more 
than a thousand full-grown individuals are sometimes poured 
out of the interior of a single univalve of moderate dimensions. 
In some large tracts of yellow sand it is impossible to detect a 
single fossil, while in other places they occur in profusion. 
The Subapennine testacea are referrible to species and fami- 
lies of which the habits are extremely diversified, some living 
in deep, others in shallow water, some in rivers or at their 
mouths. I have seen a specimen of a fresh-water univalve 
(Limnea palustris), taken from the blue marl near Parma, full 
of small marine shells. It may have been floated down by the 
same causes which carried wood and leaves into the ancient sea. 
Blocks of Apennine limestone are found in this formation 
drilled by lithodomous shells. The remains not only of tes- 
tacea and corals, but of .fishes and crabs, are met with, as also 
those of cetaeea, and even of terrestrial quadrupeds. 
A considerable list of mammiferous species has been given 
by Brocchi and some other writers ; and, although several 
mistakes have been made, and the bones of cetacea have some- 
times been confounded with those of land animals, it is still 
indubitable that the latter were carried down into the sea when 
the Subapennine sand and marl were accumulated. The same 
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