780 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



[Radium. 



Campbell Island rocks — 



No. 10. Porphyry, Perseverance Harbour 

 No. 11. Trachyte, Filhol Point 

 No. 12. „ Mount Lyell 



No. 13. Melilite basalt, Mount Lyell 

 No. 14. Dolerite, Mount Honey 

 No. 15. Limestone, Garden Cove 

 No. 16. Gabbro, North-west Bay 

 No. 17. Marble, 



2-80 

 2-64 

 1-58 

 1-61 

 0.79 

 0-46 

 0-34 

 0-28 



CONCLUSIONS. 



Since the rocks examined are derived from islands to the south of New 

 Zealand which are mostly igneous in character, the indication appears to be that 

 the distribution of Ra in the rocks of this region is in excess of that required to 

 maintain the constancy of the heat of the earth, and the necessity of an examination 

 of rocks from all places and of all age is emphasized. The mean Ra content of 

 these rocks approximates very closely to that found for others by Strutt and by 

 Eve and Mcintosh, but differs considerably from Joly's values. Further investiga- 

 tions are being made on the rocks of these antipodeal regions, and it is hoped to 

 examine the distribution of Ra in the material encountered in piercing the 

 Lyttelton Tunnel, which will give a range of time from the earliest sedimentary rocks 

 to the last flow of the volcano through the wall of whose crater the tunnel is bored. 



NOTES ON GEOLOGY OF KOCKS. 



The following notes on the geological properties of these rocks, by Mr. R. Speight, 

 F.G.S., may be of interest : — 



The two granites are both biotite -granites of ordinary type and of uncertain 

 age. The other plutonic rocks — ^the gabbros — though coming from widely sepa- 

 rated localities of the same region, exhibit marked similarities : both are olivine 

 gabbros, but that from Auckland Island is very coarse-grained at times. The co- 

 incidence of their Ra content is very striking. 



The porphyry from Campbell Island contains large numbers of zircon and 

 anorthoclase phenocrysts. 



The trachytes are all of highly alkaline type. Those from Auckland Island 

 contain a very highiji percentage of soda and a very low percentage of alumina 

 (11 per cent.) and a small quantity of free quartz : they are decidedly acid. Anortho- 

 clase is a common constituent, as well as an alkaline hornblende. The pitchstone 

 belongs to the same group, but is somewhat more basic in composition, and con- 

 tains abundant aegerine-augite microlites. The Campbell Island trachytes, accord- 

 ing to Dr. Marshall, are slightly more alkaline, and contain less iron. The rock 

 from Filhol Point contains some zirconium minerals. They are all augite -trachyte 

 with anorthoclase and occasional riebeckite and cossyrite. These rocks, together 

 with the melilite basalt, all appear to have similar amounts of Ra present. 



The other rocks from Auckland Island are basic in character, and include 

 flows and dykes. They are generally marked by a high percentage of titaniferous 

 magnetite. No. 8 is a diabase of greater age than the rest, and No. 5 a basic 



