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slime. In some situations it grows short and bushy, while in others its stems are elongated to some extent. There are three varieties of this species: (1,) with the cells greatly protruding; (2,) with the cells nearly even; and (3,) having them strongly depressed. There are two species of Meandrina found on these reefs,— M. cerebra, commonly known as brainstone from its singular appearance, and another species clearly different from the preceding, and allied to M. Dadalea of the Indian Ocean. The Madrepora cerebra grows to a large size, sometimes three feet in diameter, and is usually rounded in form; while the latter is rarely found more than six inches across, and growing in some cases within a foot of the surface on reefs, and in rock-pools even less. Two species of Astræa occur, sometimes covering the rock like a mass of sponge. These astroid corals are frequently found in a semifossil state, imbedded in the reef, and forming the base of masses of living madrepores.

On breaking into one of the reefs left dry at lowest tide, you find it composed of the following: the hard compact interior of calcareous rock, exhibiting under the lens a mass of minute portions of shell, sand, and broken coral, mixed with particles of pink-colored nullipores; the exterior presenting an irregular honeycombed appearance, some of the recesses containing sea-water and dotted with small specimens of the frilled Meandrina and smalleyed Astrea, and adhering to the sides of these miniature pools. several species of corallines and algae shooting out from beds of scarlet, and sober-colored sponges and ascidians, over which crawl the slug-like forms of the many-spotted Doris and sea-hare (Aplysia), and the massive shell-bearing Purpura deltoidea; while in the crannies and sinuous passages are snugly ensconced numbers of purple Echini and hair-clad annelides; the whole more or less covered with a mantle of iridescent sea-weeds.

Such is the state of affairs on the reef: now let us proceed to take a survey of the productions, animal and vegetable, brought thither by the current of the Gulf Stream.

As before remarked, the marine fauna of the Bermudas is almost wholly West Indian. The first, if we except a few transient visitors, are all found in the Carribean Sea. The mollusks, with one exception only, according to Tristram, are all inhabitants of the same district, while the remaining invertebrata of all orders present a similar state. Many fishes are brought to the group, sheltering and feeding amid the vast fields of gulf-weed (Fucus

natans), and several species of crustaceans reach the islands by the same source. Myriads of the Portuguese man-of-war (Physalia pelagica), the oblique-crested Velella (V. vulgaris), and two species of Ianthina (I. fragilis and I. globosa ?), with their bubble-like rafts, are cast ashore, while hundreds of the pearly Spirula (S. Peronii) float about untenanted by their rightful owners. These are all from the southward. Then ashore we find the land-crab (Gecarcinus ruricola) burrowing in the sand-hills; and running along the shore-rocks, the nimble and prettily marked Grapsus pictus, both West Indian forms. To these may be added many others all evidently descendants of an original stock brought thither by the current of the Gulf Stream.

As regards the botanical features of the islands, several trees, shrubs, and plants occur of West Indian character, some of which, springing as they do from positions close to high-water mark, denote their current origin. We may notice the calabash (Crescentia cujete), the sea-side grape (Coccoloba uvifera), the Prickly Lantana (L. aculeata), the Locust (Hymenoa coubaril), the Cochineal plant (Cactus cochinillifer); and many other species may be enumerated in support of the probable influence of the Gulf Stream. Two or three kinds of large beans are frequently found cast upon the beach: one called pin-box by the inhabitants, is the seed of a large species of trailing-vine (Entada gigantea), bearing huge scymitar-shaped pods; and is common in some of the West Indian islands, especially Jamaica, where Colonel S. Heath of the Royal Engineers informs us he has observed it growing in the mountains near the military station at Maroon Town, some two thousand feet above the sea level. Drift trees, sometimes of large size, with the roots attached, are also floated ashore; and some few years ago, according to the observant naturalist Hurdis, who resided several years in the Bermudas, two or three cedar trees of dimensions far exceeding those of any specimens to be seen on the islands, were found at some depth below the surface of a marsh which had been reclaimed from the sea, and which from their appearance were of foreign origin, and had doubtless been carried by the current from some part of the adjacent continent. These drift trees are in many instances the means of introducing pebbles and small portions of rock adhering to their roots; and it was with no little surprise that during our wanderings along the shores of the island we found these stones, of entirely different consistence to that of the sandstone in

which they lay imbedded, in the shore-rock about high-water mark; nor could we at all account for such a singular circumstance, until we were informed by a geological friend that stones had been found among the roots of trees cast away on other oceanic islands, when a clue to the mystery was at once afforded us. Thus we see in some measure the effect of ocean currents upon islands like those of the Bermudas, far removed from continents; and the case is the same in other parts of the world. Take for example the Keeling or Cocoa Islands, which are situate in the Indian Ocean at a distance of about six hundred miles from the coast of Sumatra, which owe their vegetation to seeds transported by currents from that island, Java, and Australia, and on whose shores are found stones and pebbles as in the Bermudas. Canoes of undoubted Javanese construction have also been found cast ashore; and many other instances are adduced by Chamisso, Darwin, and others, of the effect of currents upon these islands.

If such cases can be adduced of the introduction to distant islands of the ocean of whole faunas and floras, why may we not infer that in many cases islands like those of the Pacific have been peopled by the human race in a similar manner? We too frequently hear of sad cases of the survivors of abandoned vessels remaining on the ocean in open boats for a fortnight, or three weeks, or even longer, drifted along by the winds and currents in various directions. Canoes laden with people have been drifted from island to island in the Pacific, although hundreds of miles from each other, as is well known; while, according to Robertson, the fresh bodies of two men, of a race unknown to Europeans, were cast ashore, after a series of westerly gales, upon the Azores, doubtless from North or South America, proving that they had nearly completed their long drift voyage in their canoe before some untoward accident befel them and prevented their arriving alive.

We cannot therefore see, if human life can be prolonged under such circumstances, why we may not grant the drift and currents of the ocean a still greater usefulness in that of carrying to other lands a precious burden of human souls, to populate in process of time whole continents as well as islands; and, instead of looking for different centres of creation, to grant that one alone was made in conformity with the statements of holy writ.

(Read before a meeting of the Nat. Hist. Society of N. Brunswick, 29th January 1864.)

NOTES ON THE SILICIFICATION OF FOSSILS.

BY T. STERRY HUNT, M.A., F.R.S.

Fossils replaced by silica are very abundant among the paleozoic limestones of Canada. Some portions of the Corniferous limestone are little more than layers of silicified shells and corals, with a small amount of intermingled carbonate of lime; and beautiful examples of silicification are also found in various localities throughout the limestones of the Trenton and Quebec groups. The silicified fossils are confined to certain planes; unaltered calcareous shells and corals being often found in the same limestone bed, half an inch above or below a layer holding silicified fossils; and even in these the replacement is sometimes confined to a portion of the shell or coral. A careful study of a series of these silicified specimens shows the operation of three distinct processes. First, the replacement of the fossil, giving rise to an exact copy of it in chalcedonic quartz; second, the incrusting by chalcedony of a fossil thus replaced; and third, in some cases the filling up of the cavity of the replaced fossil, with chalcedony or with crystallinequartz. The corals from the Corniferous limestone present examples of the first process, and are besides often filled or lined with crystals of quartz. The same thing is to be seen in various gasteropods from the Birdseye formation. Of these, the silicified shells, from which the limestone has been removed by an acid, preserve all their superficial markings; but are often lined with crystalline quartz, although at other times filled with the sedimentary limestone. In two instances, where these shells had been fractured, the fissure has been filled up with a tissue of chalcedony identical with that replacing the shell. This chalcedony is generally found to have a botryoidal surface, and a concentric structure, which however in some cases can only be discovered by the aid of a glass. Specimens of orthoceratites from the same formation show the exterior, as well as the septa and the siphuncle beautifully replaced by silica. In some silicified gasteropods it is seen, after removing the calcareous matter by an acid, that the silicification is chiefly confined to the two walls of the shell, which are completely replaced, while the middle portion remains calcareous, or is but partially penetrated by silica. The exterior of these silicified shells is sometimes incrusted with mammillary

masses of chalcedony a tenth of an inch or more in diameter. This is an example of the second process, which is well illustrated by a fine specimen of a large and as yet undescribed species of Metoptoma from the Birdseye formation, to which. my attention has been called by Mr. Billings. It was found reposing on its base, and filled with the sedimentary limestone, which was removed by an acid, showing the interior of the shell with some small adhering Serpulæ, which are also silicified. The exterior of the shell was completely covered with a rough warty coating of chalcedony, which has evidently spread in concentric circles from certain points, and is from five to ten hundredths of an inch in thicknes. This crust, which readily separates, has been detached from a portion of the surface of the shell; which is found to have been completely replaced by chalcedony, and retains all its delicate markings. From the more frequent absence of this exterior coating of chalcedony from silicified fossils, we are inclined to look upon its deposition as a process subsequent to the replacement. In some cases however it takes place upon non-silicified specimens. Thus a Stromatopora having been cut in two, and submitted to the action of an aid, it was found that the silica was confined to an exterior crust, and to occasional grains and portions disseminated through the calcareous mass of the fossil. It is further to be remarked, that the limestone strata which contain the silicified fossils are associated with beds or masses of hornstone, in which these fossils are sometimes partially imbedded.

The facts detailed above (a part of which will be found in the Geology of Canada, p. 629) point to the conclusion that the replacement of the fossils, as well as their incrustation and filling-up with silica, took place before they were imbedded in the calcareous sediments, and that it was dependent on the presence of silica dissolved in the waters of the time. The mode in w hich the first process, or that of replacement, has been effected is however still obscure. In vegetable structures, which are very often silicified, such a replacement is comparatively rare. The pores of the wood become filled with silicious matter, while the woody fibre, in a more or less altered state, remains, and may be extracted, as Goeppert has shown, by dissolving the silica with hydrofluoric acid. This organic matter is often changed into coal, or even, according to Dr. Dawson, in some Devonian woods into a graphitic substance;

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