See! here is the soft red sandstone lying in great beds, pierced through and through with smooth round holes, just as if bored with a carpenter’s auger, big enough to admit a man’s thumb. What agency has been in operation to effect these perforations? Let us try to discover.
A few good blows with the stout hammer on the chisel-head serve to split off a great slice of the coarse red sandstone. The holes run through its substance, but they are all empty, or filled only with the black fœtid mud which the sea has deposited in their cavities. Yes; these are too superficial; they are all deserted; the stone lies too high above low-water mark: we must seek a lower level. Try here; where the lowest spring-tide only just leaves the rock bare. Ha! now we have uncovered the operators. Here lie, snugly ensconced within the tubular perforations, great mollusca, with ample ivory-like shells, which yet cannot half contain the whiter flesh of their ampler bodies, and the long stout yellow siphons that project from one extremity, reaching far up the hole towards the surface of the rock.[27]
We lift one from its cavity, all helpless and unresisting, yet manifesting its indignation at the untimely disturbance by successive spasmodic contractions of these rough yellow siphons, each accompanied with a forcible jet d’eau, a polite squirt of sea-water into our face; while, at each contraction in length, the base swells out, till the compressed valves of the sharp shell threaten to pierce through its substance.
Plate 6.
P. H. GOSSE, del. LEIGHTON, BROS.
RED-NOSE. FINGER-PHOLAS.
HYPOTHESES OF THEIR FORMATION.
Strange as it seems, these animals have bored these holes in the stone; and they are capable of boring in far harder rock than this; even in compact limestone. The actual mode in which this operation is performed long puzzled philosophers. Some maintained that the animal secreted an acid which had the power of dissolving not only various kinds of stone, but also wood, amber, wax, and other substances, in which the excavations are occasionally made. But it was hard to imagine a solvent of substances so various, and to know how the animals’ own shells were preserved from its action; while, confessedly, no such acid had ever been detected by the most careful tests.
Others maintained that the rough points which stud the shell enable it to serve as a rasp, which the animal, by rotating on its axis, uses to wear away the stone or other material; but it was difficult to understand how it was that the shell itself was not worn away in the abrasion.
Another zoologist, rejecting this hypothesis, maintained that the edges of the mantle and the short thick foot are the instruments employed; and that, though these fleshy organs seem little fitted for such work, they are really endowed with the requisite power in the shape of crystals of flint which are deposited thickly in their substance. Strange to say, however, other accurate observers fail to detect these siliceous crystals, and therefore reject the hypothesis.