4;7B Transactions. 



There seems to us only one other possible explanation — i.e., that the- 

 platinum was formerly present as a beach deposit which was subsequently 

 covered up by the detritus from the land brought down by the rivers. Such 

 beach deposits are by no means unusual, as we have just previously shown 

 in our review of the methods of occurrence, instances having been reported 

 from Oregon, Queensland, New South Wales, and so on. 



The origin of the beach-sands is conceived to be as follows : At the 

 period when the level in the south of Otago was much lower the erosive 

 action of the rivers in the neighbourhood would be greatly increased, seeing 

 that a larger fall would be provided for their waters. The interior would., 

 of course, have to be comparatively stationary, and observations in nearly 

 all areas in which elevation and depression of coastal beaches have been 

 observed tend to show that the interior does remain more or less stationar}-. 

 The Waiau River would be affected in this way. We have already seen 

 that it is a very large river, with an output equal to two-thirds that of the 

 Clutha. If we examine its course from the time it leaves Lake Manapouri 

 we shall see that it receives tributaries from the Hunter Mountains, from 

 Lake Monowai, and from the Takitimu Mountains. During a period of 

 depression, therefore, the erosion of these areas would be greatly increased, 

 and, since the rate of flow of the river would be greater, its carrying-capacity 

 would also be much greater. Consequently, at the mouth, which would 

 be further inland than it now is, much of the gravel would be deposited, 

 the remainder being deposited all along the banks. The material at the 

 mouth, by the action of the waves, would gradually be distributed along 

 the coast, so that everywhere along the borders of the land ;i bed of gravel 

 and silt would be formed. This would include minerals derived from the 

 rocks, the heaviest of which would first be dropped, and the others in tlie 

 descending order of their specific gravity. The probable existence of ;i 

 beach at Round Hill has been dwelt on already. On to this beach the 

 finer of these minerals would be carried. It is conceived that the platinum 

 has been brought in this way down the Waiau, and distributed along tlic 

 beaches. 



Let us now examine the evidence in support of this supposition. In 

 the first place, the rocks from which the River Waiau flows would have t<> 

 be platinum-bearing. If we examine the geology of the west coast of Otago 

 we see that almost the whole of the left bank of the Waiau consists of the 

 Manapouri formation of Hutton and the Kaikoura formation of Hutton. 

 Hutton, in his " Geology of Otago," in describing the former, says that it 

 is found only on the west coast of Otago from Milford Sound to Preserva- 

 tion Inlet, extending inland to Lakes Te Anau and Manapouri and to the 

 upper part of the Waiau. The rocks, he says, are composed of syenitic 

 gneiss, granuUtes, hornblende-schists, serpentine-schists, and limestone 

 (marmolite). Dr. Hector, in describing the same, says that they are horn- 

 blende-schists, felstone dykes, and serpentines. The latter, he says, wrap 

 round the formation, and in places are found on its surface. Again, Hutton. 

 in his " Geological History of New Zealand " (1899), refers to these rocks 

 as eruptives. He calls them chiefly diorites and gabbros that have acquired 

 a schistose structure by pressure. Pie says they are coincident with the 

 peridotites and serpentines occurring at intervals between Milford Sound 

 and D'Urville Island. The Takitimus, from which also tributaries come to 

 the Waiau, are placed by Hutton in his Kaikoura foiniation, which has 

 been described by Dr. Hector and Mr. S. H. Cox as filled with dykes of 

 diorite and serpentine. It is thus evident that the river comes from it 



