Cox. — On the Mineralogy of New Zealand. 447 



The next class of reefs are those which occur in the vicinity of Welling- 

 ton. The rocks here consist of ridges of slate and sandstone, probably of 

 lower carboniferous age, and these have been traversed by a series of dislo- 

 cations which cross the lines of stratification obliquely. The consequent 

 displacement appears to have indurated the sandstones and altered the 

 shales, when in contact with them, into friable cherty slates of a deep- 

 blue colour, traversed by thread-like veins of quartz (Hector, Trans. N.Z. 

 Inst., vol. ii., p. 368). These movements, when deep-seated, would doubt- 

 less be attended with the evolution of steam under great pressure, which 

 would, by traversing the cracks, carry up with it in solution whatever 

 minerals were present, and subsequently deposit them, not as they are now 

 found, but as quartz with pyrites, which would be more or less auriferous 

 according to ckcumstances. When by subsequent denudation these deep- 

 seated veins were brought under the action of the atmosphere, a decompo- 

 sition of the pyrites would ensue and free gold be left in the veins in the 

 manner in which it now occurs. In addition to the gold derived from 

 the auriferous pyrites, some must have been deposited at once in its native 

 condition or have been subjected to re-solution and precipitation, as it is 

 commonly found in a dendritic form. 



The last class of gold-bearing reefs are those of the Thames and Coro- 

 mandel districts, from which the greatest quantity of reef gold has hitherto 

 been obtained. These are of extreme interest as regards their mode of 

 occurrence. The rocks which form the matrix of these reefs are of volcanic 

 origin, and consist of various classes of a felsitic rock, raore or less decom- 

 posed, through which pyrites is very freely scattered. It appears to be 

 more or less allied to the " propyUte " of v. Kichtofen, and has been called 

 " tufanite " by Dr. Hector. These rocks rest unconformably upon the 

 slates which form the basement rock of the Cape Colville Peninsula, and 

 are in their turn overlaid unconformably by dolerite floes, and coarse volcanic 

 breccias and tufas, with which are associated kregular seams and patches 

 of coal. The whole series appears to have been tilted along a north-east 

 line, the force which thus tilted the beds having produced a series of frac- 

 tures, which, by the subsequent sinking of the hanging wall, have been 

 opened and formed subterranean water-channels, thus affording an under- 

 ground drainage to the country. Water percolating through these drains 

 has deposited quartz and, under favourable circumstances, gold from solu- 

 tion, and this gold is found, sometimes disseminated through the compact 

 portions of the stone as minute specs, and at other times entangled in a crys- 

 talline or dendritic form where the quartz is open in texture. In the latter 

 cases, more especially in vughs in the reefs, the gold is fi'equently associated 

 with Native Arsenic and Sulphides of Copper, Lead, Zinc, and Antimony. 



