Park. — Notes on a Quartz Mica-diorite. 339 



and at the same time tending to keep it at constant strength. 

 The iron nails would then by the ordinary process replace the 

 copper from the solution, forming metallic copper and a 

 soluble salt of iron. Since the solution was very dilute, the 

 deposition of copper would be very gradual, and the atoms of 

 copper would be enabled to arrange themselves symmetri- 

 cally, thus forming a regular crystalline mass. But when the 

 iron was all dissolved deposition of the copper must still have 

 taken place, and may be accounted for as follows, by con- 

 sidering the state of things in the mine : Here on the one 

 hand we have the lode continually oxidizing and dissolving, 

 and on the other hand the metallic copper previously formed 

 by the iron, and these are separated by a dilute solution of an 

 ■electrolyte. 



There are then all the elements necessary for an electric 

 current ; it is, in fact, merely a large cell, in which the native 

 copper acts as the positive plate and the lode acts as the 

 negative. The conducting liquid is so dilute that almost all 

 the copper-salt will be dissociated into its ions, the anion being 

 pure copper and the kathion being CI and S0 4 . The anion 

 will carry its load of positive electricity to the previously de- 

 posited copper nodule and deposit more copper, while the 

 kathion will carry its negative electricity to the lode and there 

 give up the CI and S0 4 . On account of the continual action of 

 the liquid by the inrushing sea these gases will be dissolved 

 or will react on the lode, and so a fresh surface of the lode will 

 be presented, thus preventing polarisation. In this way the 

 nodules of copper formed will be constantly increasing at the 

 surface of the lode-matter. The deposition will be so gradual 

 that, as before, the copper atoms will be symmetrically de- 

 posited, and will form constantly enlarging bunches of crystals 

 of copper. 



Art. XL. — Notes on a Quartz Mica-diorite from Western 



Flanks of Moehau. 



By James Park, F.G.S. 



[Read before the Auckland Institute, 25th February, 1901.] 



This rock occurs on the coast eight miles north of Waiaro, a 

 small stream flowing into the sea about five miles north of 

 Cabbage Bay. A few detached boulders, some of enormous 

 size, lie scattered along the sea-beach, and in 1897, during a 

 geological reconnaissance of the country between Cabbage 



