116 PRESIDENTS ADDRESS — SECTION C. 



normal for wind-blown particles. Accordingly he urges a recon- 

 sideration of the evidence for a marine origin of the^ material. It 

 must be noted, however, that the rock-flour on the aeolian hypo- 

 thesis i:!eed not bei considered toi have all been carried far. It 

 naay be seen nov; rising from the dried patches in the wide beds 

 of the braided rivers, at all points between the mountains and 

 the coast. 



Somewhat different problems arise in the study of the Horo- 

 whenua coastal lowland in West Wellington. (Cotton 1918 

 Adkin 1911-1919.) This has been laid down partly as a gronp 

 of confluent alluvial fans in front of the fault coast of the Tararua 

 langes, and partly as material brought down by the Manawatu 

 f^nd other rivers, distributed along the prograded coast by a south- 

 ward moving current. Cotton infers a, complex alteraticn of pro- 

 gradation and retrogradation, which he ascribed toi th© secular 

 alternation of conditions of oiverloading and underloading of the 

 long-shore curierits by detritus brought down by the rivers further 

 north. While he does not indicate a cause for such variation, 

 several possibilities may here be suggested. The first, due to 

 Morgan,* is the spasmodic eruption of vast amounts of volcanic 

 ash from the great volcanoes in the watersheds of these rivers. 

 Thei other, less direct, involves Penck's hypothesis that pluvial 

 conditions in e^tra-glacial areas are intensified during the epochs 

 of ice-advance, and diminished during the period of ice-retreat 

 in an adjacent glaciated region. If this were so, we might 

 correlatei the fluctuations in discharge of detritus by these rivers 

 with the' fluctuations in levels of the ice that appear to- have 

 occurred in the South Island. A further consideration is the 

 possible eft'ect of fluctuation of sea-level during the Ice Age, which 

 is advocated by Daly (1915), and there is also to be considered 

 the effect of very late epirogenic movements. This brings us to 

 our last topic. 



(V.) Cotton (1916) has pointed out that since- the Kaikoura 

 epoch of the differential displacement of relatively small crust- 

 blocks, there hc^ve been a series of broad epirogenic movements 

 involving equally provinces composed of many such minor blocks, 

 which movement has been, in different regions, one of elevation 

 or of depression (with the production of the rias coasts of the 

 Auckland Peninsula, Marlborough Sounds, &c.), or even of tilt- 

 ing. Exceptionally there has been considerable local movement, 

 resulting in fault-coasts, especially near Wellington (1913, 1917). 

 There has, however, been no general renewal in later times of 

 movement on the fault-lines of Kaikoura age, and the origins of 

 earthquakes felt in New Zealand are, with a few exceptions,! 



* Private communication. 



t Such as the Cheviot earthquake described by McKay (1902), or the Wellington 

 earthquake of 1855, made famous bv Lyell's account (Principles of Geology, 10th Edition, 

 1867, pp. 82-89). 



