430 Transactions. 



hood of the mine are shown on the accompanying map. They 

 are very varying in their nature, in this small valley four 

 varieties being met with — two varieties of trachytoid phono- 

 lite, one of bostonite, and one of tinguaite. The large auri- 

 ferous mass of alkaline syenite rises to within a few feet of the 

 surface here. 



Along the hill-slopes to the west there are two outcrops 

 of Tertiary sandstone indicated on the map. One of these 

 has been quarried, so that the dip and nature of the rock is 

 plainly visible. It is surrounded above and below by boston- 

 ite. The sandstone dips about 5° west, and where visible is 

 in no way contorted or faulted. The end of the drive down 

 the shaft shown on the map is walled with a sandstone crumb- 

 ling in the hands and glittering with scales of a golden-yellow 

 mica. 



In the valley in which the mine is situated a chip was ob- 

 tained from a boulder, which under the microscope exhibited 

 peculiar characters. This probably was derived from a dyke 

 of the rock, the dyke now being covered with loam, as no trace 

 of it in situ could be discovered. A description of the petro- 

 graphical characters of the rock will be found under " Petro- 

 graphy." 



The first outflow in this area was undoubtedly the bostonite. 

 The absence of any distinct flow-structures in it prevents any 

 conclusions being arrived at as to its probable vent. It seems 

 to have welled up and covered the neighbourhood with a de- 

 posit of enormous thickness. It flowed over a very highly 

 uneven sandstone surface, as the outcropping of that rock at 

 between 200 ft. and 300 ft., and its complete absence from 

 the river-bed below, proves. It would seem that an original 

 sea-cliff existed along that portion of the sandstone now out- 

 cropping. The top of this cliff now shows where the bostonite 

 has weathered away. 



Some time after the flow of bostonite the intrusion of the 

 auriferous syenite took place. This intrusion is of large extent, 

 since it occurs in fragments in the breccia thrown up at Port 

 Chalmers as mentioned above. It probably forced up the 

 sandstone in places, assuming dome-like prominences. This 

 is probably the origin of the sandstone found in the drive in 

 the mine, it being merely a portion of the main beds carried 

 mechanically upwards. It is undoubtedly after the flow and 

 consolidation of the bostonite that this intrusion took place, 

 firstly because the bostonite has been altered along its junction 

 with the syenite, secondly because this alteration is of small 

 extent owing to the solid state of the bostonite. 



Dykes were formed first of bostonite (see " Petrography "), 



