724 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. {Physiografhy , Geology. 



could not be determined ; but a boulder in a conglomerate at Camp Cove is in a 

 much better state of preservation, and contains an apparently alkaline hornblende 

 of greenish colour with strongly marked pleochroism. 



The groundmass consists of quadratic-shaped feldspars, and also a fair amount 

 of free silica (fig. \4, i). The dykes occurring at Circular Head are of similar type, 

 with slightly more quartz and a considerable quantity of chlorite, and one specimen 

 shows the characters of a coarse-grained bostonite. The feldspars are arranged in 

 sheaf-like masses, or exhibit flow structure, and anorthoclase is a prominent pheno- 

 cryst. The analyses of these two rocks show them to be of a distinctly alkaline 

 type, with a very low percentage of AlgOg. This percentage I had confirmed by 

 the analyst, who had no knowledge when they were submitted to him that one rock 

 was from a flow and the other from a dyke from the same volcanic series. The two 

 analyses, A and B, will be found also to be mutually confirmatory : — 









A. 



B. 



C. 



SiOa 







. . 66-02 



62-81 



59-52 



AI2O3 







. . 11-83 



10-36 



11-48 



FeaO., 







. 2-08 



5-92 



1-62 



PeO 







. 2-g8 



2-59 



9-93 



MnO 







. 0-17 



0-11 



0-22 



TiOo 







. 0-61 



0-71 



0-27 



CaO"^ 







. 1-03 



1-79 



4-11 



MgO 







. 0-95 



0-47 



1-03 



K2O 







. 3-73 



3-64 



2-03 



NagO 







. 8-88 



7-73 



5-31 



P2O5 







. Trace 



Trace 



None 



CO2 







. Trace 



0-17 



0-4] 



Water lost below 100° (HgO -) 



1-21 



0-81 



0-82 



above 100° (HgO-f) 



1-07 



2-44 



2-88 





100-46 



99-55 



99-63 



Specific gravity 



2-48 



2-44 



2-51 



A : Dyke, Circular Head, Carnley ; analysis by A. M. Wright. 

 B: Plow, Musgrave Peninsula, Carnley ; analysis by A. M. Wright. 

 C: Pitchstone dyke, east side of Musgrave Peninsula, Carnley; analysis by 

 A. M. Wright. 



An examination of these analyses show the rocks to be of very pronounced 

 alkaline type, approaching a pantellarite or comendite in general character, with 

 the exception of the low percentage of iron-oxides. It seems, therefore, most likely 

 that the iron-oxides "and chlorite have been derived from an alkaline hornblende 

 or augite. 



A pitchstone dyke belonging to this series was found on the east side of Mus- 

 grave Peninsula, and a boulder evidently from another similar dyke was found be- 

 low Musgrave's old camp on the western side of the peninsula. The rock is of dull 

 glassy^ appearance, and under theTmicroscope it appears as a brown glassy rock 

 crowded with slender microlites showing flow structure, especially in the neighbour- 



