Hutton. — On the Lower Gorge of the Waimakariri. 451 



That a river running in a shingle plain should make straight for a rocky 

 hill and, instead of flowing round it, should cut it in two, is a remarkahle 

 phenomenon ; and it is an account of this phenomenon and an attempt to 

 explain it that forms the subject of the present paper. 



First as to the facts which have to be explained. Both Gorge Hill and 

 Little Gorge Hill are formed of thin bedded slates and sandstones dipping 

 75° to W.S.W. at the bridge, but getting flatter higher up the river. On 

 the right bank is Gorge Hill, 363 feet above the level of the river-bed at the 

 bridge.* From the summit a spur runs towards the river in an E.N.E. 

 direction. Its altitude at the river gorge is about 270 feet. Then, follow- 

 ing the same line, comes a depression occupied partly by the river, partly by 

 gravel beds, and then, still continuing the same direction, is Little Gorge 

 Hill, 216 feet high. The depression in the slate rocks between these two 

 hills forms a steep-sided, flat-bottomed col, in which the river has cut a 

 narrow perpendicular gorge about 90 feet in depth ; the remainder of the 

 col being covered with beds of river shingle, capped by a deposit of silt 

 which, in colour and in structure, resembles the silt deposit at Lyttelton. 

 No fossils have been detected anywhere in the neighbourhood, except the 

 so-called annelid tubes in the slates. 



The plains at the north-west foot of Gorge Hill are 192 feet above the 

 river-bed at the bridge, and they extend from thence to the Malvern Hills 

 without any terraces. The plains at the north-east foot of Little Gorge 

 Hill are also 192 feet above the river-bed, and from here also they stretch 

 over to Oxford without any terraces, except some small ones formed by the 

 Kiver Eyre which have nothing to do with the subject of the present paper. 

 The river-bed, both above and below the gorge, is very wide and deeply 

 terraced ; but all the terraces, when they approach the gorge from above, 

 contract suddenly and then, below the gorge, expand again as suddenly as 

 they contracted, thus appearing like an hour-glass, the narrow neck of 

 which is at the gorge. It is evident, therefore, that the river has never 

 left the gorge since it first began to cut into the plains and form terraces. 

 However much it may have swayed from side to side, either above or below, 

 the hard rocks of the gorge have always held it like a vice ever since it 

 began to cut below the present level of the plains. But how is it that the 

 plains are at exactly the same level on both sides of the gorge hills ? And 

 how is it that the river has cut through the hill instead of running round it ? 



* The heights of the two Gorge Hills are taken from the trigonometrical survey of 

 Canterbury as given by Dr. von Haast in his " Geology of Canterbury and Westland," 

 p. 476 ; the levels of the terraces are from the survey for the Oxford and Sheffield rail- 

 way, kindly supplied me by Mr. G. P. Williams. All the levels here given are calculated 

 from the bed of the river at the bridge, taken as the datum. This datum is 808 feet above 

 high-water mark at Sumner. The figures on the plan show the height in feet above the 

 river-bed at the bridge. 



