PRESIDE^^T'S ADDRESS — SECTION C. 115 



(1917) concurs with Marshall in regard to the absence of any 

 indication of glacial eiroisioii on the great volcanoes in the centre 

 of the North Island, but the possibility must be considered that 

 Recent eruptions may have more or less obscured the erosional 

 forms developed during Pleistocene times. 



(IV.) Concurrently with this denudation there has been much 

 sedimentation du-ring Pleistocene times. The studies of two of 

 these regions are of particular interest. Speight (1910) has added 

 greatly to Von Haast's 1879 valuable exposition of the origin of 

 the Canterbury Plains. This coaisists of a great gravel formation 

 resting unconformably on the Kowhai (" Early Pleistocene ") 

 gravels in North Canterbury, or upon the Notocene rocks of South 

 Canterbury. They extend for 160 miles along the coast, and reach 

 a maximum width of 30 miles. Their seaward slope is compara- 

 tively steep, for they reach an elevation of 1,500 feet at their 

 western margin. Examination of the records of artesian bores 

 show that they extend to a depth of at least 600 feet, and were 

 deposited as confluent alluvial fans upon a slowly subsiding pied- 

 mont surface. The occurrence of fossiliferous mai*ine beds, and of 

 layers of lignite, intercalated at various horizons in the gravels, 

 indicates the fluctuation of the shore line. This is not necessarily 

 due to inequalities in the rate of subsidence. On the Ninety Mile 

 Beach the detritus brought down in vast quantities by the rivers, 

 is exposed toi a strong northerly drift along the coast. Where the 

 supply of shingle fails, the sea encroaches on the land. Hence 

 the tendency will be for the retrograding of a shore south of a 

 river mouth, and its prograding nqrth of the mouth. Since the 

 courses of rivers discharging across alluvial fans is subject to 

 frequent change, the areas of prograding and retrograding of the 

 coast-line must accordingly have varied from time to time, and the 

 intercalations mentioned might thus be produced. A notable 

 example of the variation in the course of a river on an alluvial 

 fan is that of the Waimakariri, which, though now entering the 

 sea north of Banks Peninsula, threatens to return to its former 

 outlet south of the peninsula, and embankments have been placed 

 to protect the town of Christchurch , which lies between the two 

 channels. 



We may here note as an additional feature of interest the 

 occurrence of Icess along the coast line frona Banks Peninsula to 

 Oamaru. A discussion arose as to^ whether it is truly wind-borne 

 loess or a marine silt, but the former view, heTH by Heim (1905) 

 is that now generally supported, the source of the material being 

 found in the dried rock flour in the valle3'^-trains below the glaciers 

 of the Canterbury Alps, which was conveyed to the coast by the 

 foehn-like north-west wind. Recently, however. Wild (1919) has 

 pointed out that the grain-size in a sample of the deposit which 

 he examined, is greater than that of the typical loss of Iowa and 

 Nebraska, or than that which, according to Udden (18'94), is 



