318 



J'ronKactions. 



position of the highest peaks with regard to the mountain axis of the 8outb 

 Island is to be observed further south, where Mount d'Archiac (9,279 ft.) 

 in the Tavo Thumb Range, Malte Brun in the Maltebrun Range, and Mount 

 Cook itself lie to the east of the main watershed, and excel in elevation 

 the neighbouring peaks on it. The crest of the range also lies far to the 

 east of the structural or tectonic axis of the Island, Avhich no doubt follows 

 up through the schistose belt between the sea and the present main range 

 about twenty miles from the west coast. This suggests that the present 

 configuration has been the result of excessive erosion acting for a long 



Fig. 1. — -Map of Mount Areowsjuth District. 



period of time on the western wing of the geanticline of which the range- 

 has been built, far more profoundly than it has acted on the eastern wing.. 



(6.) Relation to Rain jail and Conditions of Erosion. 



The mountains in this locality lie right across the direction of the 

 prevailing westerly winds of this latitude, and the bulk of the moisture is 

 intercepted on their western slopes. The conditions are exactly the same 

 as these further north at Otira, which, according to the records of the 

 meteorological station recently established, has a yearly rainfall of a Little 

 over 200 in., while at Bealey, about twelve miles away in a straight line, it 

 is only 100 in. Although no statistics are available for the Rakaia region, 

 the effect is clearly visible in the character of the plant covering, whieb 

 changes from the rain forest of Westland to the markedly xeroph}^ic 

 tussock steppe of the region to the east of Mount Arrowsmith. Inter- 

 mediately there is the totara forest of the Upper Rakaia, which has followed 

 the rain just across the main divide from the montane rain forest containing 

 totara on the hisher hill country of Westland. 



