Hutton. — The Formation of the Canterbury Plains. 467 



gorge the river-bed is very wide and beautifully terraced, and 

 the same occurs below the gorge ; while in the gorge itself the 

 river is confined within a narrow channel. 



Now, how can we explain this ? Evidently the river must at 

 one time have run at a higher level than the top of the gorge. 

 At that time nearly the whole of Gorge Hill would have been 

 buried by sand and gravel beds, through which the river cut its 

 way down. We can hardly doubt but that the high-level gravel- 

 patches near Springfield are also part of these same gravel-beds, 

 for they go up to about the same height. But how have the 

 intermediate portions been removed ? They could not have been 

 removed by the river itself, because to do so the river must have 

 left the gorge and cut a new channel at a lower level round the 

 bill. If it had done this it could not possibly have regained its 

 old level in the gorge, for that would be on a higher level. But 

 the gravel -beds have evidently been removed by water — they 

 could not have been blown away by the wind — and if they were 

 not removed by the river the sea is the only agent left. 



Now, take the lower gorge of the Waipara close to where it 

 runs into the sea. This gorge has been cut through a spur from 

 the neighbouring hills, which the river pierces instead of going 

 round, as it certainly would have done if the river-bed had been 

 marked out under the existing conditions. Here also, as in the 

 case of the Waimakariri, we must assume that the river at some 

 former time ran at a higher level than the spur through which 

 it cuts, and that the greater part of the gravel-beds over which 

 it then ran have been subsequently removed by the sea. 



If we go outside the Canterbury Plains to look for collateral 

 evidence we find it at Amuri Bluff, where a raised beach has been 

 described by Mr. A. McKay, at a height of 500 ft. above the 

 sea, containing marine shells of still living species. Again, at the 

 mouth of the River Conway gravel terraces go to 300 ft. above 

 the sea, but no shells have been found in them. And lastly, at 

 Motunau marine shells of recent species are found in abundance 

 at 150 ft. above the sea. 



I cannot, therefore, agree with Sir Julius von Haast, in his 

 report " On the Formation of the Canterbury Plains " (Christ- 

 church, 1864), that these plains are entirely due to river-action. 

 But I must believe that, although the materials of which they 

 are formed were brought down from the mountains by the rivers 

 and accumulated under river conditions, during a long period of 

 subsidence the contour of the surface has been much modified 

 by the subsequent action of the sea, which swept away a con- 

 siderable portion of the upper beds when the land was probably 

 1,000 ft. lower than at present.* 



*See, however, Haast in the Trans. N.Z. Inst., vol. vi., p. 421. 



