462 Transactions. 



less rounded, smooth, and only in rather rare cases flat. This plain looks 

 therefore, much like one of fluviatile deposition, such as occurs in Otago, 

 in the Waikato district of Auckland, and, according to some authorities, 

 in Canterbury. Further evidence and opinions as to its origin will appear 

 later on. 



A continuation of this p^.ain is found east of the Longwood, intersected 

 here and there by stream.s flowing from the range. The most pronounced 

 in character, however, of all the plains is that formed by the Waiau River. 

 This river during nearly all the latter half of its course flows between 

 banks composed partly of pebbles and partly of limestone or calcareous 

 sandstone. For a distance of two m.iles in some places, in others three, 

 on either side of the river flat alluvial land extends, passing gradually into 

 a series of hilly spurs, and from there to the mountains. It is this flat that 

 constitutes the Waiau Plain. It is very wide at the mouth (about a mile), 

 and gradually tapers backwards, but it extends for many miles up the 

 river, and south of Lake Manapouri the land is so flat that marshes have 

 been formed. Evidently it is a plain of fluviatile deposition, the uniformity 

 of surface being produced by the deposition of gravel and silt as the fall of 

 the river has diminished. Pronounced terraces have been seen in places 

 on the banks, and, since the flow of water is so great that these could hardly 

 have been formed by changes in the course of the river, it is legitimate to 

 assume they are due to a small elevation of the surrounding district, especi- 

 ally as the depth of the river is very considerable. 



No other jjlains worthy of mention occur. 



The rivers must now be considered. These are : (a.) The Pourakino, 

 which rises amongst the easterly spurs of the Longwood, flows generally 

 in a southerly direction, and after a rather tortuous course empties itself 

 into Jacob's Estuary near Riverton, It is chiefly interesting on account 

 of the gold-washing that goes on near its source and as far as the point 

 where the river enters the plains. (6.) The Ourawera, which, rising in the 

 southerly spurs of the Longwood, flows due south, and, with a tributary 

 from Lake George, enters Wakapatu Bay. It is along the course of this 

 river that the gold and platinum grains are found which form the basis 

 of this paper, (c.) The Rurikaka River, which has its source near the 

 base of Round Hill, and, flowing in a south-westerly direction close past 

 Pahia Township, enters Foveaux Strait, {d.) The Waimeamea, which, 

 having its source on the western slopes of the range, with a tributary system 

 very like that of the Pourakino, flows in a south-westerly direction across 

 the plain, and after a remarkably tortuous course across the flat country 

 enters Te Waewae Bay. (e.) The Orawia, a tributary of the Waiau, may 

 also be taken as a separate stream. It takes its rise in the comparatively 

 hilly country to the north of our northern boundary, flows also towards 

 the south-west, and after a to tuous course joins the Waiau opposite Bald 

 Hill. 



In the case of the last three rivers — viz., the Rurikaka, the Waimeamea, 

 and the Orawia — and to some extent the Waiau, which we shall describe 

 next, it will be noticed that they fall very conveniently into the classifi- 

 cation (adopted by Professor J. C. Russell in his " River Development ") 

 of streams which have their source in mountain-ranges and flow across 

 broad j^lains to the sea. Such streams may be divided, he says, into three 

 divisions — the mountain tract, where the streams flow impetuously in 

 narrow depressions ; the valley tract, where the stream widens and is 

 bordered by flood-plains ; and the plains tract, where the grade is still 



