130 REPORT— 1891. 



granular and porphyritic — which show in undecomposed rem- 

 nants in it at the foot of the chffs in the neighbourhood of the 

 dykes ; the dark-grey rock occurs also in large masses on top 

 of the promontory. Thin sections of both these rock-varieties 

 will be more specially noticed further on. 



Eegarding the discovery of the second locality of occurrence 

 of the coarsely-porphyritic rock, it happened as follows : At 

 the time the Portobello samples were under examination, Air. 

 A. C. Purdie, senior, on seeing his son's specimens, affirmed 

 that he had in his possession a specimen of the same kind of 

 rock found on the Pine Hill spur, close north of Dunedin. 

 The specimen w^as produced, and the identity in character of 

 the rock with that from Portobello seen at a glance. Mr. A. 

 Purdie, junior, thereupon examined the indicated locality 

 where his father had found his specimen, and soon discovered 

 boulders of the rock accumulated in the road that passes up 

 the middle of the Pine Hill spur — the boulders having been 

 collected from the cultivated paddocks on either side of it. On 

 my subsequent examination of the place I found that the area 

 of distribution of the boulders, before cultivation of the pad- 

 docks commenced, might have been, perhaps, 15 chains in 

 length by 4 to 5 chains in width over the here rather broad- 

 backed spur. The rock could not, however, be discovered 

 anywhere in situ within the indicated area. The Pine Hill 

 spur, it must here be mentioned, terminates about a quarter of 

 a mile south-west of the boulder -locality, falling rather 

 steeply from a height of about 250ft. towards the valley of the 

 Water of Leith, the main watercourse of the district, and 

 forming, for some distance, a vertical cliff at foot. From this 

 terminating point it gradually rises through a distance of about 

 four miles in a north-easterly direction, with several short 

 steep ascents, whilst sending a number of lateral spurs into 

 the valleys on either side, to the Pine Hill, a transversely- 

 extended mountain -ridge about 1,300ft. in height. Near 

 above the boulder-locality there is a massive outcrop of horn- 

 blende-augite-andesite — a rock which seems also to prevail in 

 the valleys near around the foot of the spur, with this excep- 

 tion : that in the vertical cliff along the Water of Leith there 

 is an intrusion of common basalt and dolerite which does not 

 extend to the top of the spur. No evidence of any dyke of 

 the nepheline rock traversing the spur and hidden at the 

 boulder-site being tlms discoverable, Mr. A. Purdie made 

 several excursions up the spur, but, though carefully searching, 

 could not find any more of the specific rock-boulders, till at 

 last he was successful in discovering massive outcrops of the 

 rock itself on the steep slope of the Pine Hill, facing Dunedin, 

 and he also ascertained that the entire hill is composed of the 

 rock, which, however, becomes more finely porphyritic towards 



