Imagens das páginas
PDF

in the South Esk basin, the coal strata, with the variegated sandstone above them, were uplifted 2100 feet above the actual level of the basin.

FOURTH EPOCH.

Above the series of strata, and the unstratified masses, composed of materials differing in origin, age, and mineralogical and chemical character, are found, both in New South Wales and Van Diemen's Land, here and there, multifarious accumulations, some of which, as sand, gravel, pebbles, &c, are seen to rest upon the surface, in the form of loose gravel or sand, or transported matter; others, as the elevated beaches, are disposed in indurated horizontal beds; some like the osseous breccia, at Wellington, fill the crevices of the rocks; but the greater part lie in confused masses, and in a state of partial decomposition, either filling the bottoms, or lodged against the sides of the valleys. We shall now briefly review the forms under which these different accumulations present themselves.

LOOSE MINERAL SUBSTANCES.

Amongst the transported matter, gravel, sand, and fragments of rocks, are found oxides, phosphates, sulphurets, and arseniates of iron, oxides of titanium, molybdiate of lead, cornelian, opal, agate, and agglomerated pebbles of compound minerals. The range of the last-named substances, scattered, as we find them, over the surface of the two colonies, combined with the fact of their being composed of minerals varying extremely in specific gravity, and of their exhibiting mostly an elliptical and flat shape, leads to the belief that the surface of the colonies has been gradually rising, and had been for some time exposed to the attritive action of shallow water, before it arrived at its present height above the sea.

[graphic]

ELEVATED BEACHES

Are disposed, at wide intervals, along the present coast of the two colonies: they present commonly horizontal beds, and occur at various heights above the existing sea; some showing marks of greater antiquity than others. Thus the elevated beaches at Lake King (Gipps Land) are seventy feet above the sea: they are composed of an indurated reddish clay and calcareous paste, containing ostrea and anomia, which are different from the existing specie; while the elevated beaches seen on the southern shore of New South Wales, between Cape Littrap and Portland Bay, contain ostrea of the present time, agglutinated by a gritty paste. The elevated beach which forms Green Island, in Bass's Straits, is again but a comminuted mass of shells, and rises to the height of 100 feet: that of the south-west point of Flinders Island exhibits the same character. The two last beaches are abutted against granite, sienite and greenstone.

At ten miles south of Cape Grimm, and west coast of Van Diemen's Land are found, at 100 feet above the present sea, elevated beaches, similar to those of Bass's Straits, and approaching in structure to a coarse and porous sandstone. The beds of these beaches are within the zone of clay slate of the second epoch, and in the vicinity of basalt and trachytic conglomerates.

At Table Cape, the raised beach contains —

Dentalium,
Venus,
TurriteUa,
Tellina,
with Sponges- and Corals.

It rests upon basalt, and is seventy feet above the level of the sea.

The character of these elevated beaches, and their occurrence in localities widely separated, furnish important additions to the evidence collected in other parts of the world, not only respecting the agencies which still operate in uplifting the earth's surface, but to the local and confined manifestations of such upheavings.

Osseous Breccias.

Among the instances of brecciated accumulations in clefts or caves, the most remarkable is the osseous breccia of the "Wellington Valley. The caves in which it is contained are similar to other limestone caverns: the nature of the breccia, in regard to the aggregation of the organic remains and brecciated rocks, does not present any characteristic marks of difference from other similar compounds; and the presence of both kinds of matter in this locality appears as difficult to account for here as the ossiferous caves in Europe.

The Wellington caves are nevertheless of great interest and importance, recording periods of terrestrial revolution in this country similar to those which have happened in other parts of the world; and presenting to us the remains of some of the land animals which were the first inhabitants of Terra Australis.

All their remains, hitherto discovered, consist of detached bones much broken, and very frequently in fragments. The genius, however, of Cuvier and Owen, to whom a broken tooth or vertebra has often sufficed for deciphering the form and character of the entire animal, has supplied the deficiency and the incompleteness of the Australian records.

It is thus that the Australian bones have been found to belong to extinct animals, some of which are unknown to naturalists, as the Diprotodon, and Nototherium; — some, as the Macropm, ffypsiprymnits, Phascolomys, Dasyurus, Thylacinus, presenting but typical forms of the existing species.

Availing myself of the liberality of Professor Owen, who has contributed the largest share towards our knowledge of the Australian fossils, I shall, in another place, lay an abstract before the reader of some of his most interesting papers relating to the subject.

DEBRIS ACCUMULATED IN VALLEYS.

Throughout the two colonies, the valleys are characterised by the more or less excellent soil they afford to agriculture. These soils differ much in different places, and possess characteristics by which they may be classified. Upon what that classification depends; what are the productive powers of each class; how far industry has availed herself of the virgin soils; and to what degree those under cultivation are susceptible of improvement,—will be discussed in the Agricultural Section, which closes this volume. But, independent of soils, the valleys possess fossil trees of great interest; some, as at Dart Brook and at Lake George, New South Wales, in fragments, imperfectly fossilised; some again, as in the Derwent Valley, Van Diemen's Land, in the form of truncated trees or stumps, perfectly opalised, imbedded in porous and scoriaceous basalt and trachytic conglomerate.

No where, to my knowledge, is the aspect of fossil wood more magnificent than at the place last mentioned; and no where is the original structure of the tree better preserved: while the outside presents a homogeneous and a hard glassy surface, variegated with coloured stripes, like a barked pine, the interior, composed of distinct concentric layers, apparently compact and homogeneous, may be nevertheless sepa

L

rated into longitudinal fibres, which are susceptible of subdivision into almost hair-like filaments.

These valuable remains were examined, contemporaneously with my own visit, by Dr. Hooker, of H. M. Ship "Erebus," then bound on the South Polar expedition; and I shall quote, in the language of that zealous and distinguished botanist, the description of the characters which the fossil trees present.

"The most remarkable circumstance," says Dr. Hooker, describing one of the opalised trees, "is the manner in which the outer layers of wood, when exposed by the removal of the bark, separate into the ultimate fibres of which it is composed, forming an amianthus-like mass on the ventricle of the stump in one place, and covering the ground -with a white powder, commonly called, here, native pounce. The examination of a single concentric layer from this part, shows that it may be detached from the contiguous layers of the preceding and following year's growth; there being no siliceous matter infiltrated into the intervening spaces. A portion of each layer is found to have a second cleavage, not concentric with, but in the direction of its radius, or of a line drawn from the centre to the bark of the tree. Such a cleavage is to be expected from the fact, that it is in the direction of the medullary rays that traverse every where the woody tissue. Each of these laminae is of extreme tenuity, of indeterminate length, and of the breadth of the layers of wood; and is formed of a single series of parallel woody fibres, crossed here and there by the cellular tissue of the medullary rays, which do not generally interfere with their regularity. These plates, again, are separable into single minute fibres, which are elongated tubes of pleurenchyma or woody tissue, tapering at either end into conical terminations of indefinite length. They lie together in

« AnteriorContinuar »