118 Transactions. 



two instances emphasize the shallow-water nature of the strata in the 

 Nukiimaru - Kai Iwi section, and they show also that there were tempo- 

 rary oscillations in the level of the land whilst the deposition of fhese rocks 

 was in progress. 



The continuity of the stratigraphical succession is, however, well shown 

 by the nature of the fossil mollusca which are contained in the rocks, for 

 they display a nearly, uniform gradual change as one proceeds northward 

 along the coast-line, and therefore into lower strata. It has already been 

 suggested that the small pebbles in some of the strata came from the north- 

 west of Nelson, but no suggestion has yet been made as to the source of the 

 great mass of the blue clay, which constitutes by far the greater part of 

 these younger Tertiary sediments. One of the most notable features of the 

 mineralogical composition of this blue clay is its highly micaceous nature. 

 The mica is muscovite, and whenever a coarser stratum than usual occurs 

 the mica flakes in particular are of such a large size that the only origin 

 that can reasonably be assigned to them is a granitic rock. There is at 

 the present time no such rock known to occur in the North Island, and 

 unless some large pre-existing mass has been submerged, or covered up 

 by sediments, we must look to the South Island for the rock-mass from 

 which all this sediment was derived. There is no reason to think that any 

 previously existing granite mass in the North Island is now concealed from 

 view, and it is to the South Island that our attention is at once directed. 



In the north-west of Nelson there is now a large area of country which 

 is composed of a granite. It is suggested that it is from this rock that 

 the younger Tertiary sediments of the Wanganui district were derived. 

 It is true that so far as that granite is known there is not a great deal of 

 muscovite in its composition ; but up to the present time little petro- 

 graphical work has been done on the rock, and it is quite possible that a 

 portion of the granite, which crops out over an area of some 800 square 

 miles, is more micaceous than the few specimens that have been closely 

 examined. It is true also that on its seaward margin the granite has a 

 superficial covering of Tertiary rocks of a greater age than the Wanganui 

 series of sediments. The granite mountains rise, however, to a height of 

 6;000 ft., and no Tertiarj^ sediments are exposed at a greater height than 

 2,000 ft. It is a fact also that no granite pebbles have been found in the 

 coarser strata that often occur in the Wanganui sediments. This objection, 

 however, is not a strong one, because the granite is notoriously friable, and 

 no pebbles are found on the long beach of Farewell Spit, which is mainly 

 composed of detritus from the granite. 



At the present time there is no material on the beaches of the Wanganui 

 coast that could have a granite origin assigned to it, and the depth of the 

 north-west entrance of Cook Strait is too great to allow of the drift of any 

 such material from the South Island, especially when the strong inflow and 

 outflow of tides through the strait is considered. • If the origin of the sedi- 

 ment is to be traced to the Karamea granite, as is here suggested. Cook 

 Strait must at that time have been closed, and a continuous beach must 

 have extended from Kahurangi Point to the Wanganui area. 



The thickness of the sediments is a matter of great importance in the 

 subject of this paper. The direction of the strike is, on the whole, so 

 constant, and makes such a considerable angle with the coast-line, that 

 it is at once evident that in a distance of twenty miles along the coast a 

 great thickness of sediment must be passed through. Taking the average 

 of the dip and strike mentioned above (strike 70° and dip 4|^°), it is found 

 that the thickness of rocks between Castlecliff and Kai Iwi is 950 ft., the 



