446 Transactions. 



than probable that it is derived from the magma whence flowed 

 the tinguaites, phono! ites, basanites, and kenytes of the remaindei 

 of the Peninsula, and in these rocks so far absolutely no sign of 

 pyrites has been discovered. A differentiation of a magma 

 so complete as to include all the pyrites in one outflow seems 

 improbable. The fact that all the other rocks were either 

 ejected through dykes or volcanoes seems rather to show that 

 the free communication with the air enabled the sulphides to 

 escape, being either carried up mechanically with the steam 

 present, or else being vaporised and escaping with the reduction 

 of pressure consequent upon entrance to a surface-connected 

 fissure. Whether the precious metals have also escaped or not 

 is to be decided only by careful assays by fine methods on large 

 bodies of these rocks, and theoretical considerations seem to 

 show that traces of them, at least, will be found 



The district is comparable to that of the Thames and Coro- 

 mandel goldfields. There the country rock is andesite, and the 

 existence of gold in this country rock is a disputed point. In 

 the Otago Peninsula, however, the gold occurs comparatively 

 richly in one rock at least ejected from the magma beneath, 

 and the formation of auriferous lodes in this district was pre- 

 vented, either on the lateral - secretion or ascension theories, 

 only by the absence of lode-forming fissures and the circulation 

 of a suitable gold-dissolving solution. 



EXPLANATION OF PLATES IX-XIII. 

 Plate IX. 



Fig. 1. Pseudamusium huttoni, reduced size, 4 : 3, with profile views. 

 Fig. 2. Microphotograph of syenite, showing resorption zone round horn- 

 blende. 



Plate X. 



Fig. 3. Microphotograph of basalt, crossed nicols. 

 Fig. 4. ,, phonolite, crossed nicols. 



Plate XL 



Fig. 5. Microphotograph of undetermined rock, crossed nicols, showing 



augite and soda amphibole. 

 Fig. 6. Microphotograph of tinguaite. 



|Plate XII. 



Fig. 7. Microphotograph of tinguaite, crossed nicols. a, hornblende nest ; 



b, a?gerine twin. 

 Fig. 8. Microphotograph of bostonitc, crossed nicols. 



Plate XIII. 

 Map of Harbour Cone. 



