by Charles Hedley (1893)
The explanation offered by Wallace in "Island Life," and generally accepted, is: (1) commencing the biological history of Australia with the Cretaceous era, that Eastern and Western Australia were then totally severed; (2) that Eastern Australia was at that time quite devoid of a typical Australian terrestrial fauna and flora, which was then confined to Western Australia; (3) that a large area of what is now the floor of the Tasman Sea was upheaved, and nearly, or quite, connected New Zealand with Australia, whereby the flora and fauna, then existing in Eastern Australia, were enabled to colonise New Zealand; (4) that this hypothetical bridge then sank, isolating the New Zealand colonists, and afterwards dry land appeared between Eastern and Western Australia, upon which the characteristic Australian forms first crossed from west to east.
Apart from the difficulty they are supposed to satisfy, little or no evidence is advanced for the support of these propositions. That a Cretaceous sea separated Eastern from Western Australia may be granted, but that at any time Western Australia possessed a monopoly of characteristic Australian plants or animals is improbable. Recent discoveries show that the dry land representing Western Australia in Cretaceous times was much less than Wallace supposed, and than appears in the sketch map on p. 497 of the second edition of "Island Life." In the region explored by the Elder Expedition, "an area of Mesozoic formation extends as far as long. 123°."2 The shallow inland Cretaceous sea was studded with islands, large and small, which served the fauna and flora as stepping-stones in their migrations from west to east and from east to west. Some of these are now [[p. 188]] represented in Central Australia by the Macdonnel, Musgrave, and Everard Ranges;3 in Queensland by an extensive area of Palæozoic schists, extending almost from the Gulf of Carpentaria to beyond Cloncurry, reappearing in the south as the Grey and Stokes Ranges,4 and yet again in New South Wales as the Barrier Range. If allowance be made for denudation, more islands probably then existed than geological maps now indicate. Tertiary fossils from Victoria, N.S.W., and Queensland show as marked an Australian facies as recent plants and animals. Such are the various species of Banksia from the Lower Miocene.5 The very characteristically Australian remains preserved in the Darling Downs' deposits cannot, says De Vis, be considered as of later date than Early Pliocene.6 Finally, many genera and species among recent plants and animals essentially Australian are confined to Eastern Australia. Wallace correctly remarks that West Australia is richer than the East in peculiarly Australian plants, but when, as described later, the archaic Queensland flora was submerged and almost extinguished by the Papuan invaders, great numbers of such peculiarly Australian plants must have perished in Eastern Australia.
More in need of confirmation than the preceding propositions stands the theory that a large tract of the Tasman Sea connecting Australia with New Zealand was upheaved, and when it had served its purpose conveniently, subsided at the close of the Cretaceous. Except about the twentieth parallel, where a bank no deeper than 1,300 fathoms connects the Great Barrier Reef with New Caledonia, the shores of Eastern Australia everywhere front deep water of over 2,000 fathoms, to the north the abyss of the Coral Sea, to the south that of the Tasman Sea. The geological history of this coast, as opposed to that of New Zealand, indicates great stability; such a vast elevation and subsequent depression as Wallace demands could scarcely have occurred without leaving signs decipherable by geologists. If the upheaval was local instead of general, it must, to satisfy the theory, have taken place between Bowen and Rockhampton, where the Caledonian Barrier Bank abuts on the Queensland coast. No consequent distortion of the strata appears to have been there observed by local geologists.
Upon detailed examination, it appears that although the fauna of New Zealand sometimes approximates to that of Queensland, yet it could not have been derived therefrom; that, in short, the relation is not that of mother and daughter, but that of sisters. An analysis of the Australian land shells shows the range of the operculated forms [[p. 189]] to be restricted to the coast of Queensland, and that, proceeding from south to north, the group becomes gradually richer in species and in genera. In the New Zealand fauna the operculates are represented by a tenth of the snail fauna as compared to none in Australia, except Queensland, to one-sixth in Queensland, and one-third in New Guinea. So far our investigation conforms to Wallace's theory, and as that demands an origin in Australia for the New Zealand fauna, so we expect the operculate land mollusca of New Zealand to be descendants of those of Queensland. Here, however, facts rebel against the theory, the New Zealand species being ranked under Lagocheilus, Realia, and Hydrocena, while the Queensland ones are contained in Georissa, Truncatella, Pupina, Callia, Pupinella, Hedleya, Ditropis, Diplommatina, Leptopoma, and Helicina; than which two faunas could hardly be more distinct.
Most European writers who have touched on the zoo-geography of Australia have described the fauna and flora as falling into a temperate and a tropical division, which again subdivide into eastern and western sections. A little real experience proves these divisions to be quite artificial. The dry interior, for example, is everywhere inhabited by the same plants and animals, regardless of latitude or longitude; examples are, the great red kangaroo among mammals, the plain turkey, the maller hen and the rosy cockatoo among birds, the frog Notaden bennetti, the lizard Lygosoma monotropis, and the snakes Pseudonaja nuchalis and Hoplocephalus nigriceps, among plants the predominance of salt-bush, spinifex, gidya (acacia), and Frenela. On the eastern seaboard, the difference between north and south is that between a conquering and invading fauna and flora and the indigenous population where not exterminated or obscured by them. The types encountered by a traveller in tropical Queensland, or rather in that narrow belt of tropical Queensland hemmed in between the Cordillera and the Pacific, all wear a foreign aspect. Among butterflies the Ornithoptera, among reptiles the crocodile, among birds the cassowary and rifle bird, among mammals the tree kangaroo and the cuscus, and among plants the profusion of epiphytic orchids and of palms, all point to a northern origin. In the heart of a great Queensland "Scrub" a naturalist could scarcely answer from his surroundings whether he were in New Guinea or Australia.
Late in the Tertiary Epoch, as I read the record, Torres Straits, now only a few fathoms deep, was upheaved, and across this bridge there poured into Australia a stream of Papuan life. Between the coastal range and the sea as far as the tropics the irruption flowed in undiminished strength; on reaching the border of N.S.W. the cooler climate diminished its vigour, and at the Clarence River, N.S.W., with few exceptions, it found its southern limit. Within this area grow side by side, like oil and water--touching yet not commingling, two distinct vegetations, the dense Papuan jungle called "Scrub" by the Queenslanders, which has usurped every rich volcanic upland and [[p. 190]] every fat alluvial plain, and the lightly timbered "Forest" of acacias and eucalypts confined to the inferior soils. As sharp a line is drawn between "Scrub" and "Forest" as a European may see between an Alpine meadow and a thick pine wood.
In considering the contour of the floor of the Western Pacific in relation to the distribution of species, we are greatly hampered by want of information. Too few and distant are the deep-sea soundings to determine the trend of the numerous banks and troughs of this region. Something can, however, be deduced from the "Challenger" discoveries. When that vessel ran a line of soundings across the Coral Sea, she found that the temperature of the soundings diminished down to 1,300 fathoms, below which depth it was stationary, proving that no cold stream from the depths of the Central Pacific or Antarctic Oceans could penetrate and chill this basin;7 from which it is to be inferred that no gap deeper than 1,300 fathoms crosses the rampart extending from the Solomons to New Zealand. This region, in contrast to Australia, is one of great volcanic activity, and there are evidences of great fluctuation of levels in the past. If we consider that this track was ridged up by the contraction of the floor of the South Pacific, the fact would be accounted for that the various earth-waves of this plateau--for example, the Southern Alps of New Zealand--all curl, or have their steepest face towards Australia; and this argument, if granted, would render more probable the former existence of a continuous land-surface from the Solomons to New Zealand. It would explain the undisturbed condition of the Australian Tertiary and Mesozoic beds, which escaped the shocks of contraction, as compared with those of New Zealand which received them. Holmes and Hinde assume from the contained sponge remains that the siliceous beds of Oamaru, New Zealand, were formed at depths of not less that 6,000 to 9,000 feet in Eocene seas8; while Guppy considers that since Post-tertiary times the Solomon Archipelago has been upheaved at least 12,000 feet.9 The vertebrate fauna of the Solomons evinces a recent descent from Papuan types, apart from which it shares with the New Hebrides and New Caledonia that remarkable poverty of mammalian and reptilian forms so distinctive a trait of New Zealand. Besides this negative evidence may be adduced the instructive distribution of Placostylus. This large Bulimoid snail forms one of the most striking components of the snail fauna of New Zealand, Lord Howe Island, New Caledonia, the New Hebrides, the Solomons, and the Fijis. This distribution appears to be in no way connected with trade winds or ocean currents. On the supposition that the remoter colonies of Placostylus were seaborne emigrants, it would be difficult to explain how, when Lord Howe was populated from New Zealand [[p. 191]] or New Caledonia, that the emigrants who had successfully traversed the wide and shallow portion of the Tasman Sea should be stayed by the narrower but profound waters from reaching Australia. Similarly, a narrow but a deep strait intervenes between Fiji with numerous species and Samoa with none, between the Solomons where the genus is well represented and the Louisiades where it is absent. The beaches of Queensland, as I can testify from personal observation, are strewn by a constant drift of pumice accompanied by coco-nuts and pearly nautilus shells. The coco-nuts might have floated from any tropical island in the Pacific, the nautilus shells are only derivable from the narrower limits of the Solomons, the Fijis, and the New Hebrides, while the pumice must almost certainly be the product of the active volcanoes of the New Hebridean group. It is therefore obvious that in the Western Pacific the chief route of drifting objects is that of the trade winds from N.E to S.W. To an objection that the range of Placostylus might be due to transmarine migration, it is a sufficient answer to observe that this genus extends beyond and across, but not parallel to, the direction of the principal agency of dispersal in this region. Both birds and plants contribute evidence of the homogeneity of the fauna and flora of these islands, and of their distinctness from those of Australia. Among the former may be quoted Merula and Aplonis, and especially the distribution, past and present, in Lord Howe, Norfolk Island, and New Zealand of Nestor, Platycereus, Notornis, and Ocydromus.10 Of the botany of Lord Howe Island it is especially to be remarked that, whereas on Wallace's theory it should, lying nearest to Australia, be most akin to that region, yet "those typical Australian families the Leguminosæ and the Myrtaceæ are barely represented, whilst the Proteaceæ are said to be wholly wanting."11
Upon these grounds I conjecture that an ancient continent, separated on the west from Australia by the abysses of the Coral and of the Tasman Seas, is represented by the Solomons, the Fijis, the New Hebrides, New Caledonia, Lord Howe, and New Zealand, with its outlying islands--an area that I have elsewhere12 proposed to call the Melanesian Plateau, and upon part of which Forbes has more recently conferred the name of Antarctica.13
In conclusion, I would contend that New Zealand is associated with the Solomons and the New Hebrides, firstly, as a member of their volcanic system; secondly, by community of fauna and flora; whereas to Australia it is related not at all physically, and to a foreign and intrusive element biologically; and that a theory which derives the fauna and flora of New Zealand primarily from these archipelagoes and remotely from New Guinea, necessitates fewer unproved assumptions than that which derives them from Australia.
1. J. D. Hooker, "Introductory Essay
to the Flora of Tasmania," pp. lxxxviii.-ix.