388 Transactions. 



robbing the less extended valleys of the supply of water at their heads 

 and cutting in behind them. The result of this will be that the spurs which 

 stretch down from the summit will broaden out as they reach lower levels, 

 and the valleys established on their peripheral portions will in many cases 

 be short. This feature is well displayed in the spurs which reach out in 

 a northerly and westerly direction into the plains, where wave action has 

 exerted but little effect ; but on the outer rim of the volcano, where sea 

 action has been intense, the broader terminal portions have been removed, 

 and the effect is not so pronounced, since the lower portions of the short 

 streams have been cut away, and the water either enters the sea by short 

 steep ravines or by falls. 



As these valleys run in the direction of the dip of the beds and at right 

 angles to the strike, they exhibit the special features of transverse valleys 

 ■ — that is, they are trench-like in character, with steep sides ; there is 

 always a tendency to cut subsequent valleys at right angles, especiallv 

 in their higher portions, but owing to the variation in the direction of dip 

 and the discontinuity of particular layers these do not exhibit the regularity 

 usually displayed by valleys cut in sedimentary strata. This may explain 

 the amphitheatre-like form which characterizes the heads of many of the 

 valleys, and where this does not occur it explains the branching heads of 

 the valleys. This peculiarity has been noted by J. D. Dana with regard 

 to the volcanic island of Tahiti,* where he states that the valleys of that 

 dissected island are frequently narrow in their lower portions but open 

 out into distinct amphitheatres at their heads. This gives an appearance 

 resembling a crater or caldera, and it is this which probably influenced 

 Haast so strongly in suggesting that the Little Eiver and Pigeon Bay 

 Valleys were really calderas, and the sites of independent volcanic vents. 



Owing to the dominant valleys enlarging the upper part of their basins 

 into an amphitheatre-like form, the heads of the adjacent smaller valleys 

 are robbed of their proper supply of water — that is, the amount rightly 

 belonging to the whole of the sector of the volcano which they should drain, 

 and not the outer portion of that sector only. Although the smaller valleys 

 may initially have been truly radial in orientation, in process of time they 

 depart slightly from that direction and their heads point towards the high 

 bounding ridge of the adjacent large valley. Further, owing to the more 

 pronounced erosion in the dominant valley, the walls tend to encroach 

 on the higher reaches of the smaller valley and to capture some portion 

 of its higher reaches, which were primarily eroded by the water which dis- 

 charged by means of the smaller valley. It thus exhibits what may be 

 called a recessive character. As a result the smaller valleys are often 

 headed by distinct saddles. This is well seen to the east of the Little River 

 Valley. In the former direction, towards Peraki, all the valleys reaching 

 down to the small indentations of the coast rise not from the crater-ring 

 of Akaroa, but from the high eastern wall of the Little River Valley ; while 

 to the west, between this valley and the large Kaituna Valley, we have 

 first Price's Valley and then Birdling's Valley reaching back successively 

 to the valley-wall of Little River, the second valley as it touches the crest 

 farther up being far the longer of the two (see Plate XXIV). In both these 

 cases the subordinate valleys are headed by depressions in the dominant 

 ridge, not deeply incised, it is true, but the effect is still visible, and in 



* J. D. Dana, Characteristics of Volcanoes, 1890, p. 376. 



