302 Transactio'us. — Geology. 



land, which extended to an altitude exceeding that of the present mountain 

 chain by at least 4,000 to 5,000 feet, and that they attained their maximum 

 extension coincidently with the maximum of elevation. They also lend 

 strength to the assumption (founded on other independent grounds) that 

 during the period of maximum elevation the land of wliich the present New- 

 Zealand islands proper are the chief remnant had a quasi-continental extension, 

 chiefly to the eastward, and embraced, at least, the chain of iskmds above 

 referred to. And they further justify us in attributing the disappearance of 

 the glaciers in question to a depression of the land continued up to a 

 comparatively recent period, a circumstance which, I think, is chiefly indicated 

 by the following facts, namely : — That the larger number of the valley lakes 

 which still exist above the terminal moraines of glaciers of the first order in 

 those portions of the range in question which intervene between Mount 

 Cook and the Spencer Mountains (as for example. Lake Sumner on the line of 

 the Hurunui River), have been only partially filled up with alluvium, 

 although the rivers which feed them are all shingle-bearing torrents ; whilst, 

 on the other hand, the lake which succeeded the great glacier of the Dillon 

 has actually been filled with alluvium within the period which its outlet has 

 occupied in cutting down the moraine dam to a depth of 35 feet only, for a 

 distance, having regard to the general fall of the valley, of little more than 

 half a mile. 



With regard to the probable time at which the upheaval referred to took 

 place I can offer but few observations. So far as I can understand from the 

 reports of the Geological Survey, we have no evidence of any upper marine 

 pliocene beds in the Middle Island, whilst the upper portions of the miocene 

 series are found at elevations varying from 1,200 to 1,800 feet above sea level. 

 I therefore assume that the elevation in question commenced at the close of 

 the miocene period, and that the more recent pliocene deposits within the 

 Novo-Zealandian Province would only have been found on the outside 

 boundaries of the quasi-continental area which existed when the elevation 

 referred to attained its maximum, and were submerged during the subsequent 

 subsidence of the land. The total elevation most probably approached 

 5,000 to 6,000 feet, the subsequent depression exceeding that by at least 

 from 1,200 to 1,500 feet. At what time the dejiression ceased it is difficult to 

 say, but it probably continued in pleistocene times, when a re-elevation of the 

 land again took place. 



The period which I have ventured to assign for this great oscillation of 

 level would, no doubt, be considered immense if it could possibly be counted 

 in years, but is certainly not too great for the effects produced. That the 

 connection between the main islands and the Chatham Group must have been 

 severed at a comparatively remote period is indicated by the fact that much 



