374 



the plateau in the lines of least resistance, so that the plateau is at last cut 

 up into sharp ridges and peaks, on which snow can no longer rest in qiiantity 

 to maintain the glaciers, which consequently disappear, leaving only the 

 moraines to mark the successive steps of the process. This is however quite 

 insufficient to explain the origin of the deep excavations in the hard rock, as 

 above described, and the difference in the amount of the excavation on the 

 opposite sides of the axis, irrespective of the character of the rock excavated, 

 (which is in fact the most resisting in its character on that side where the 

 excavation has been apparently the deepest) points to an unequal subsidence as 

 the origin of these basins. This subsidence has been most rapid in the central 

 and western part of the range, so that in the case of a long valley, like that 

 occupied by the Wakatipu lake, the slope became gradually reversed, and 

 what was at first the higher part of a glacier-excavated valley, has become a 

 depression without an outlet. Gradually this depression is being filled up, 

 by the material brought down by the streams, and carried from the moraines 

 higher up the valleys, as represented by d in the section ; but this material 

 cannot, especially where resting on the rocky floor of the valley, have 

 been subjected to the action of running water after it has been deposited 

 in the still waters of the lake, and therefore fails in one of the essential 

 processes for the formation of auriferous leads, namely, the concentration of 

 the gold from the lighter particles of the detritus. 



From these considerations it is evident that it is only round the margins 

 of rock basins, or in positions above the level of the notch in the margin 

 over which the water escapes, that we can expect to find auriferous leads. 



High on the eastern slopes of the mountains, in the position marked e on 

 the section, are found patches of gravels belonging to the newer system which 

 drained the mountain range previous to this unequal subsidence, and before 

 the excavation of the deep gorges by the extended glaciers of the Pleistocene 

 period ; and the gold in most of the alluvial workings in Otago, can be traced 

 to such patches of older drift. 



I will now describe briefly the mines which have been worked in New 

 Zealand for the less precious metals, and mention the localities where " lodes" 

 have been discovered. 



The Island of Kawau, where the earliest opened mine is situated, 

 was first purchased by the North British Investment Company, about 

 1841, as a cattle run. It lies four miles from the main land, thirty- 

 seven miles north of Auckland, is about three and a half, by three and a 

 quarter miles in extent, and, from the Admiralty survey, appears to have an 

 extent of about 5200 acres. The island consists of slate rocks which form two 

 principal masses of high land, separated by an E. and W. depression, partly 

 occupied by Bon Accord harbour, and continued eastward by several valleys 

 with wide alluvial bottoms. In each of these masses hills rise from 500 feet 

 to 600 feet altitude, the summits marking the outcrop of mineral veins in 

 most cases. The strike of the older rocks is very varied in direction, but 

 ranges between N.E. and IST.W. The dip has a prevailing westerly direction, 

 generally at a high angle. All these rocks are, however, cut by cleavage veins 

 and faults, that give them a false trend to ]S\ 320° E. In this line lie the 

 mineral lodes, and " belts " of mineralized rock, four of which are known. 



The first discovery was made at Manganese Point, where the lode shows 

 as follows : — ■ 



a. Soft decomposing slate. 



b. Red jasparoid slate, encircled with iron and manganese. 



c. Soft red rock containing the same ores. 



d. Hornstone . 



e. Blue slates. 



