418 Transactions. — Geology. 



Notes by Alexandek McKay, F.G.S., Assistant Geologist. 



There are three distinct formations of Pala30zoic date iu 

 Stewart Island. Of Secondary or Older Tertiary rocks there is 

 not a trace. Outside the northern entrance to Port Pegasus 

 there is a small islet formed of coarse and rudelv-stratified 

 granitic material, which I am inclined to refer to the Pliocene 

 period. All the other deposits that have as yet been observed 

 are obviously of Pleistocene or Kecent date. These latter are 

 of considerable extent in the district between the head of 

 Paterson's Inlet and the west coast, and along the valley of 

 Freshwater Eiver. Away from the coast-line little is known 

 respecting the geology of the north and north-east parts of 

 the island ; and what we do know of the formations along the 

 coast-line is mainly due to the researches of Sir James Hector, 

 who touched at Stewart Island in 1863 while engaged in ex- 

 ploring the south-west and west portion of the Province of 

 Otago. More recently I have added something to a know- 

 ledge of the geology of the district around Half-moon Bay and 

 the shores of the eastern part of Paterson's Inlet, ai:id have 

 collected from bushmen and prospectors some information re- 

 specting the west coast of the island north of Mason's Beach. 



As I have mapped it, it would appear that in this part the 

 country is mainly formed of granite, intersected by dykes of 

 later date. Where I examined the district around Half-moon 

 Bay, and along the shore of the eastern part of Paterson's 

 Inlet, the rocks are gneissic schists, traversed in an east to west 

 or north-west direction by massive intrusions of hornblendic 

 syenite. These syenitic intrusions in every respect resemble — 

 nay, to all appearances, are identical with — the syenites of 

 Bluff Hill, on the mainland, and I am inclined to think that, 

 however altered, the other rocks of the district are not greatly 

 different in age. The less-altered rocks on the south side of 

 Paterson's Inlet would, it appears to me, support this 

 assumption. 



From this district come two of the most conspicuous 

 minerals in Mr. Skey's list. These are beryl and tourma- 

 line. Both of these minerals are found together in afelspathic 

 band, forming a selvage to one of the syenitic intrusions 

 already mentioned. The tourmaline occurs in considerable 

 plenty ; the beryl is not so common, but yet not rare, and 

 occasionally fine large crystals are to be found. The syenitic 

 band runs nearly east-and-west along the north shore of the 

 Inlet, and, from what I could gather, getsnmch more massive 

 as it is followed to the westward. 



Along the south side of Paterson's Inlet the rocks are of 

 a different character, being subschistose and not so much 

 altered ; but in their structure it may be traced that originally 



