The fissures through which the lava rose may be seen in many places,
forming what are called DIKES.
(FIGURE 133. Pecten jacobaeus; half natural size.)
No shell is more conspicuous in these Sicilian strata than the great scallop,
Pecten jacobaeus (Figure 133), now so common in the neighbouring seas. The more
we reflect on the preponderating number of this and other recent shells, the
more we are surprised at the great thickness, solidity, and height above the sea
of the rocky masses in which they are entombed, and the vast amount of
geographical change which has taken place since their origin. It must be
remembered that, before they began to emerge, the uppermost strata of the whole
must have been deposited under water. In order, therefore, to form a just
conception of their antiquity, we must first examine singly the innumerable
minute parts of which the whole is made up, the successive beds of shells,
corals, volcanic ashes, conglomerates, and sheets of lava; and we must
afterwards contemplate the time required for the gradual upheaval of the rocks,
and the excavation of the valleys.
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