HuTTON. — The Geological History of Neiv Zealand. 175 



animals would have been killed off in their southern localities, 

 for there is no place near New Zealand to which, in Pleisto- 

 cene times, the subtropical flora could have temporarily re- 

 treated and then returned after the cold was over. 



The same may be said of almost the entire faunas and 

 floras of the islands lying to the south of New Zealand. Yet 

 we find in the Auckland Islands a peculiar genus of duck 

 (Nesonetta) which cannot fly, and in xlntipodes Island a pe- 

 culiar parroquet (Cyauorliamphus jcnicolor) which has almost 

 lost its powers of flight. These birds must have been de- 

 veloped on the islands where we now find them, and the 

 process must have been a slow one ; yet during the whole of 

 that time the islands could not have been covered with ice. 

 We may extend this argument to other islands in the Ant- 

 arctic Ocean, such as Kerguelen Land and the Crozets. 

 These possess several peculiar plants and animals, and it is 

 certain that the islands could not have been covered with ice 

 since the first appearance of their present floras. A general 

 reduction of the temperature of the whole Southern Hemi- 

 sphere being therefore out of the question, we must look for 

 other and local causes for the extension of the glaciers. Two 

 theories have been advanced — one is that our mountains 

 during the great glacier epoch were flat-topped, forming 

 plateaux on which large masses of snow collected ; the other 

 is that the mountains stood at a greater altitude than at pre- 

 sent, due to a general elevation of the whole Island. 



Now, passing over the question whether large snow- 

 ' covered plateaux necessarily imply large glaciers— they do not 

 do so in Norway — we are met with the fact that most of our 

 river-valleys had been cut down to their present level before 

 the Oligocene period, for rocks of that age fill several of them 

 nearly or quite to the bottom. For example, it is certain that 

 in the Eocene period the Eakaia Eiver ran at a lower level 

 than it does at present. As this is an important point I will 

 give the proofs of my statement. 



In the valley of the Kakaia, opposite the east end of Lake 

 Coleridge, there is an outlier of Oligocene limestone called 

 Eedcliff. It is lying almost horizontal in its original plane of 

 deposition in a lateral valley on the south side of the river, 

 and is, no doubt, a fragment of a set of beds which once filled 

 all that part of the valley. Now, as this limestone passes 

 under the gravels and descends below the present level of the 

 river, it is evident that when the Kakaia scoured out the 

 valley in the Eocene period it must have been running at 

 a lower level than at present, for it now runs on the top of 

 alluvial gravels which partly fill up the whole valley. Also 

 the junction of the limestone with the Palaeozoic rocks must 

 mark the limit of the valley of the Eakaia at that place when 



