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Show ~80 lMDEDDING OF MARlNE TESTACJ~A. [Ch. XVII. popotamus, ox, and horse, with occasionally, perhaps, some intermixture of terrestrial and lacustrine shells! Such, we are taught, would be the memorials of a marine deluge sweeping over our continents! We are, however, willing to admit that they who invent causes without reference to known analogies, are guilty of no inconsistency when they claim some license in the use which they make of their extraordinary agents. If we allow them to " call spirits from the vasty deep " to do their bidding, and to uplift colossal chains, like the Andes, suddenly within the historical era, we must not complain that the effects of such mighty powers are not always such as the analogy of the ordinary laws of Nature would have led us to anticipate. Marine Testacea.-The aquatic animals and plants which inhabit an estuary are liable, like the trees and land animals which people the alluvial plains of a great river, to be swept from time to time far into the deep. For as a river is perpetually shifting its course, and undermining a portion ofits banks with the forests which cover them, so the marine current alters its direction from time to time, and bears away the banks of sand and mud, against which it turns its force. These banks may consist in great measure of shells peculiar to shallow, and sometimes brackish water, which may have been accumulating for centuries, until at length they are carried away and spread out along the bottom of the sea, at a depth at which they could not have lived and multiplied. Thus litt~ral and estuary shells are more frequently liable even than freshwater species, to be intermixed with the exuvire of pelagic tribes. After the late storm of February 4, 1831, when several vessels were wrecked in the estuary of the Forth, the current was directed against a bed of oysters with such force, that great heaps of them were thrown alive upon the beach, and remained above high-water mark. Many of these oysters, as also the common whelks (buccina), which were thrown up with them, in a living state, were worn by the long attrition of sand which had passed over them as they la/' in their native Ch. XVII.] lMllEDDING OF MARINE 'l'ESTACEA. ~81 be~, and which had evidently not resulted from the mere actiOn of the tempest by which they had been cast ashore. :From these facts we may learn that the union of the two parts of a bivalve shell does not prove that it may not have been transported to a certain distance; and when we find shells worn, and whh all their prominent parts rubbed off, they may still have been imbedded where they grew. It sometimes appears extraordinary when we observe the violence of the breakers on our coast, and see the strenoth of the current in removing cliffs and sweepin<>' out new cha~nels 0 ' that many tender and fragile shells should inhabit the sea in the immediate vicinity of this turmoil. But a <>'reat number of the bivalve testacea, and many also of the tu~binated univalves burrow in sand or mud. Thei) solen and the cardium for example, which arc usually found in shallow water ncar th; shore, pierce through a soft bottom without injury to their shells; and the pholas can drill a cavity through mud of considerable hardness. The species of these and many other tribes can sink, when alarmed, with considerable rapidity, often to the depth of several feet, and can also penetrate upwards again to the surface if a mass of matter be heaped upon them. The hurricane, therefore, may expend its fury in vain, and may sweep away even the upper part of banks of sand or mud, or may roll pebbles over them, and yet these testacea may remain below secure and uninjured. 'Ve have already stated that at the depth of nine hundred and fifty fathoms between Gibraltar and Ceuta, Captain Smyth found a gravelly bottom, with fragments of broken shells carried thither probably from the comparatively shallow parts of the neighbouring straits, through which a powerful current flows. Beds of shelly sand might here, in the course of ages, be accumulated several thousand feet thick. Dut, without the aid of the drifting power of a current, shells may accumulate in the spot where they live and die, at great depths from the surface, if sediment be thrown down upon them; for, even in our own colder latitudes, the depths at which living marine |