176 Transactions. — Geology. 



the limestone was formed. If, therefore, any great lateral 

 denudation had taken place since that time, the line of 

 junction between the two rocks ought to stand out as part of a 

 prominence. But it does not do so ; consequently, the lower 

 portion of the Eakaia A'alley cannot have been greatly enlarged 

 since the Eocene period. This is confirmed by the fact that 

 on the southern slopes of Mount Algidus, in the Upper Eakaia, 

 there is another outlier of Tertiary marine rocks, showing that 

 there also the valley was very deep long before the Pliocene 

 period. 



It is therefore very unlikely that a great plateau in the 

 upper part of the Eakaia Valley has been lately removed ; and 

 we may say, generally, that as the rivers of the South Island 

 had cut such deep valleys before the Oligocene period it seems 

 impossible, from what we know about river erosion, to believe 

 that any large plateaux could at that time have been in exist- 

 ence — that is, none to which we could attach any great im- 

 portance.* If also, as we have seen, the New Zealand Alps 

 were formed in the middle of the Jurassic period, and have 

 been exposed to the action of the weather ever since, plateaux 

 of any size could not have existed from the Jurassic to the 

 Pliocene and then have rapidly disappeared, especially at a 

 time when, by the hypothesis, they were protected by a 

 covering of perpetual snow. 



This plateau hypothesis failing, we are left with that of 

 elevation to account for the phenomena ; and it has been cal- 

 culated that an elevation of between 3,000 ft. and 4,000 ft. 

 would, at the present day, be sufficient to expand our glaciers 

 to their former dimensions.! That the New Zealand Alps 

 did formerl)' stand higher than they do now we have direct 

 evidence in the deep fiords of south-west Otago and Marl- 

 borough, which must have been excavated when the land was 

 considerably elevated. The greatest depth recorded in the 

 West Coast Sounds is 1,728ft., in Breaksea Sound; but in 

 many places no bottom was reached with the line used, and 

 we may safely assume that when the valleys were scooped out 

 they stood more than 2,000 ft. higher than they do now. 

 And this agrees fairly well with the quite independent esti- 

 mate that an elevation of 3,000 ft. or 4,000 ft. would be 

 sufficient to reproduce all the phenomena. In Canterbury 

 also we find evidence of a former elevation, for in sinking 

 a well in Christchurch a quantity of solid timber was found 

 at a depth of more than 400 ft., which must either have grown 

 on the spot or have been brought there by a river. How deep 

 the shingle-beds of the Canterbury Plains go we do not know. 



* See Ann. Mag. Nat. Hist., series 5, vol. 15, p. 91. 

 t Trans. N.Z. lust., vol. viii., p. 385. 



