232 Physical Geography of 



north and south, augments as we advance towards their centre, having 

 their greatest lateral extension near Banks' Peninsula, where, in a 

 direction from east to west, they stretch a distance of nearly 50 miles 

 to the base of the mountains. The Pacific Ocean is their boundary on 

 the eastern side, where a long shore stretches in a line nearly from 

 south-west to north-east — from Timaru to Double Corner being only 

 interrupted by the volcanic system of Banks' Peninsula, which 

 rises so conspicuously in the middle of that low shore, and to the 

 existence of which a great portion of the loose strata composing these 

 plains mainly owes its preservation from the destructive agencies of the 

 waves and currents. The western boundary is formed by the outrunning 

 spurs of the Southern Alps, having, as I have pointed out previously, 

 hj their disintegration, offered the material for the present con- 

 figuration and other physical features of those plains. In their 

 greater bulk they consist of the accumulation of post-pliocene torrents. 

 Having had their glacier sources much nearer to Banks' Peninsula 

 than in present times, the latter were able to throw the boulders, 

 shingle, sand, and ooze, carried along with them, not only in greater 

 masses but also on steeper slopes than the present rivers crossing 

 them can do, for reasons given in the geological portion. These post- 

 pliocene deposits of huge rivers, have covered with an almost uniform 

 gradient the palaeozoic, volcanic, or tertiary rocks, composing here. 

 the former sea bottom. 



On my arrival in Canterbury, I was informed that the Canterbury 

 plains had only such a slight gradient, that at the foot of the 

 mountains they barely reached an altitude of 300 feet, and I was there- 

 fere somewhat surprised when the barometer revealed to me the fact, 

 that this was a popular error, and that the upper portion of these 

 plains was at least 1500 feet above the sea-level, having thus a fall of 

 about 45 feet in the mile, or 1 in 117. Owing to causes, fully to be 

 explained in the geological portion of this Eeport, the large rivers 

 which built up their huge shingle-fans side by side, afterwards lowered 

 their beds in course of time, so that at the intersection of the fans 

 with the present river-bed, new shallow fans were, and are still, being 

 formed. Below this line of intersection, some of the finest and most- 

 fertile agricultural land in Canterbury is situated. Although the 

 Canterbury plains terminate at the sea coast near Double Corner, they 

 continue across the middle "Waipara for ten miles further north, being 

 first about four miles broad and gradually getting narrower, ending at 

 the Omihi saddle, which leads into the "Waikari, a tributary of the 



