248 DE. C. CHILTON ON THE SUBTEEEANEAN 



subterranean fauna. Mr. Suter points out that the shell of this specimen showed no approach 

 to the dead-white colour of the Potamopyrgus, which is no doubt truly subterranean. 



At the same time and from the same pump Mr. Smith obtained one or two specimens 

 of CalUopius subterraneus. 



VI. The Canterbury Plains and their Underground Waters. 



All the localities from which subterranean Crustacea have been as yet collected in 

 New Zealand are situated on the Canterbury Plains, and in order to clear the way for 

 the discussion of the probable origin of these forms it will be convenient to state first a 

 few facts about the formation of the plains and as to their underground waters. Much 

 of what follows is taken from the late Sir Julius von Haast's ' Geology of the Provinces 

 of Canterbury and Westland, New Zealand ' [53]. In speaking of the plains formed on 

 the eastern side of the Southern Alps he says : — 



" The most prominent amongst these are the Canterbury Plains, which, by their 

 position, nature, and general characteristics, form a prominent feature of this island, and 

 are already the centre of a rich, industrious, and large population. They begin at the 

 dolerite plateau of Timaru, and stretch without interruijtion to Double Corner, iu a 

 general direction from south-west to north-east, with a length of about 112 miles. Their 

 breadtli from a few miles at both extremities, north and south, augments as Ave 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 so 

 great a portion of the loose strata composing these plains 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, by 

 their disintegration, ofi'ered the material for the present configuration and other physical 

 features of the plains. In their great 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 steej)er slopes than the 

 present rivers crossing them can do, for reasons given in the geological portion. These 

 post-pliocene deposits of large rivers have covered with an almost uniform gradient the 

 palaeozoic, volcanic, or tertiary rocks composing here the sea-bottom " [53, p. 231]. 



The Canterbury Plains slope towards the sea at the rate of about 40 feet to the mile 

 for the first fifteen or twenty miles from the mountains, and at an average of 24 feet to 

 the mile for the remainder of the distance to the sea. This may be illustrated by the 

 following figures taken from Sir Julius von Haast's ' Geology ' [53, p. 403], showing the 

 fall of two of the rivers in the basins of which subterranean Crustacea have been 

 found : — 



