THE ORIGIN OF THE FAUNA AND FLORA OF NEW ZEALAND. 259 
second is elevation in combination with the subsidence below 
the sea of Central Australia.* (3.) The third is the plateau 
hypothesis alone, the land being at the same level as now. It 
is supposed that these plateaux have been reduced to sharp 
ridges by the erosion of the glaciers, and thus the retreat of the 
glaciers is accounted for.f (4.) The fourth is elevation alone, 
the retreat of the glaciers being caused by subsequent depres- 
sion.} 
These hypotheses resolve themselves into three, viz :—Sub- 
sidence of Central Australia, broad plateaux, and elevation— 
taken either singly or in combination. We will examine each of 
them. 
The subsidence hypothesis is thus explained by its author. 
“ One cause of the greater extent of the New Zealand glaciers 
Emcee fs % is that the elevation of the New Zealand mountains was 
probably coincident with the submergence of the low land inthe 
interior of Australia, which is covered with a post-pliocene 
marine formation. The equatorial north-west winds would thus 
impinge on the New Zealand Aips without, as at present, being 
deprived of a large amount of their aqueous vapour by passing 
over the arid plains of Australia, and the condensation of snow 
by the mountains would be therefore very much in excess, and 
consequently the glaciers much larger than at present."§ This 
hypothesis is similar to one long ago proposed to account for the 
former extension of the Swiss glaciers by the submergence of the 
Sahara. But in our case it has been shewn that the hot north- 
west winds, as well as the cold south-west winds, are parts of 
westerly cyclones,|| and that they are saturated with moisture 
when they reach New Zealand. That our north-west winds owe 
their heat and dryness to local causes, and not to the arid plains 
of Australia, has been explained by Dr. Knightq and by Mr. 
Barkas.*, The subsidence of Central Australia might possibly 
decrease their temperature and therefore decrease the amount of 
aqueous vapour held by them, but this could not possibly in- 
crease the amount of snow on the mountains. 
The plateau hypothesis was proposed many years ago by 
Rendu, to account for the former extension of the glaciers of 
Switzerland, but it never obtained many adherents. It was shewn 
that the effect of plateaux is to diminish, not to increase, the 
* Hector, in a letter to Sir J. Hooker, dated 15th July, 1864, in Lyell’s Princi- 
of Geology, 12th ed., Vol. I., p. 243, and Trans, N.Z. Institute, VI., p. 385 
(1873). 
+ Haast, Q.J.G.8S. X XI, p. 135 (1864), and Geology of Canterbury and West- 
land p.p. 372-4 (1879); in his Geology of Canterbury (p. 376) Dr. v. Haast says 
that I was the former chief exponent of the theory that the extension of our glaciers 
ocurred during a partial submergence of the land, Ido not know to what Dr. v. 
Haast alludes. | The submergence that I have always advocated was in the pleisto- 
cene, after the glacier epoch was over. 
£ Dobson, Trans, N.Z, Inst., IV., p. 340, and VI., p. 294; Travers, Trans. 
ee iust.; VI., p. 299. 
§ Trans. N.Z. Institute, VI., p. 385. 
|| On the Principles of New Zealand weather Forecast, by Commander Edwin, 
R.N.; Trans, N.Z. Inst., XII, p. 4o 
4] Trans, N.Z, Inst., VIL, p. 470,—*, N. Z. Journal of Science, L, p. 576. 
