igo NATURAL SCIENCE. Sept., 



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 seas 8 ; 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. Resides 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 



'Voyage of H.M.S. "Challenger," narrative, vol. i., p. 519. 



6 Journ. Linn. Soc, vol. xxiv , pp. 178 and 255. 



9 H. B. Guppy, "The Solomon Islands, their Geology, etc.," p. 126. 



