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Here also we find most frequently specimens of lamellibranchiate molluscs, with both the valves united, showing that they belonged to this sea of the Upper Crag, and were not washed in from an older bed, such as the Coralline, in which case the ligament would not have held together the valves in strata so often showing signs of the boisterous action of the waves.
The Snail, and other one-shelled molluscs, poke their heads out of the shell when feeding or moving. Oysters and their two-shelled cousins cannot do this, for the simple reason that they have no heads! In some places you see that the rocks at low tide are covered with Mussels. In dense black masses they cling to the rocks; and, though heavy waves bang them like so many hammers, they stick tight.
Whenever we went near the water among the rocks, we saw large fish darting about, of every colour and shape; huge, long eels gliding in and out between the rocks, and fierce, voracious sharks pursuing their prey. There were a great variety of molluscs; indeed, the whole shore was composed of shells.
But this foot is a most wonderful boring tool, fitted with a hard file. Hard rocks and wood are perforated by these little molluscs. Indeed, they are a positive danger, for they pierce the wooden piles of piers, and weaken them. They cannot pierce through iron, however, and so iron plates or nails are used to protect the piles from their onslaughts.
Woodward has shown that the same law holds good with sea-shells, but, from the wide distribution of most molluscs, it is not well displayed by them. Other cases could be added, as the relation between the extinct and living land-shells of Madeira; and between the extinct and living brackish water-shells of the Aralo-Caspian Sea.
Our theatres are undeveloped beings, pulpy, pappy molluscs, which can never bring forth a man. I must refrain from saying any more on this head; it might easily lead me to writing another book of four hundred pages, and the writing of books I am determined to abandon in preference to producing a work of art.
Woodward has shown that the same law holds good with sea-shells, but from the wide distribution of most genera of molluscs, it is not well displayed by them. Other cases could be added, as the relation between the extinct and living land-shells of Madeira; and between the extinct and living brackish-water shells of the Aralo-Caspian Sea.
The descent of the Ampullaria, and other fresh-water molluscs, into the mud of the tanks, has its parallel in the conduct of the Bulimi and Helices on land. The European snail, in the beginning of winter, either buries itself in the earth or withdraws to some crevice or overarching stone to await the returning vegetation of spring.
To reduce the table within limits, I have grouped together all the lower forms of life in the animal table, viz., the sponges, corals, encrinites, and molluscs. It is sufficient to say that these appear in all the rocks except the very oldest the Caelenterata beginning, and the Molluscoids exhibiting an early order in brachiopoda, which seems to be dying out.
These just hatched molluscs, though aquatic in their nature, survived on the duck's feet, in damp air, from twelve to twenty hours; and in this length of time a duck or heron might fly at least six or seven hundred miles, and would be sure to alight on a pool or rivulet, if blown across sea to an oceanic island or to any other distant point.
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