734 SUBANTARCTIC ISLANDS OF NEW ZEALAND. [Physiography, Geology. 



for the most part between andesine and labradorite : this gives certain of the rocks 

 an andesitic character which the analysis does not support. Analysis No. 1 (given 

 above) is from a rock of this character. The marked absence of any F.M. minerals, 

 except augite and olivine, is very noteworthy. Hornblende is very scarce, even in 

 the earlier flows. 



These series may be taken as typical of the basaltic rocks of the southern por- 

 tion of the group. As a rule, the coarser-grained types seem to be more common 

 than the fine ones^ though the finer types seem to be relatively more abundant in the 

 earlier flows. This statement may, however, have to be modified after further 

 investigation. Samples of the basalts of the northern end of the group were col- 

 lected by the German Transit of Venus Expedition in 1874, and were thoroughly 

 described by Hartmann ;* and there is also a reference to the basalts of Port Eoss 

 in the geological report of the " Discovery " Expedition. f Nothing is known about 

 the rocks of the middle portion of the main island — i.e., the part north of Norman's 

 Inlet and south of Port Ross — but there is reason to expect they are the same as the 

 rocks at the north and the south ends of the group. 



It is almost impossible to assign an age to these basalts, but from their fresh- 

 ness and from the well-preserved form of the caldera-walls it may be inferred that 

 the eruptions took place in middle or even late Tertiary times. 



VOLCANIC DYKES. 



The volcanic dykes at Carnley may be classified as follows : (1) Trachyte 

 dykes of an alkaline character found penetrating gabbro and granite and not found 

 elsewhere ; (2) porphyrites of a relatively more acid type found penetrating gabbro 

 and the porphyrites and diabases of the lower basic series ; (3) diabases and basic 

 porphyrites found in gabbro and basalt ; (4) dolerites found in the lower basic 

 series. This classification indicates the relative age, with the exception that (3) 

 and (4) may be more or less contemporaneous, and date from the last phase of the 

 volcanic action. The trachytes and more acid porphyrites have been referred to 

 previously, but the third series has not been mentioned. 



The dykes of this series were observed on the shore of Carnley Harbour, near 

 Camp Cove, on the end of McClure Head and Circular Head, and on the north shore 

 of Adams Island. Those observed had a northerly strike, varying from north- 

 east to north-west, but the harbour-foreshore was not covered sufficiently to determine 

 their general orientation. The diabases are very fine grained, and without the 

 typical diabase structure ; they are rarely ophitic, and are occasionally much more 

 decomposed than the basic rocks they penetrate, and for no apparent reason. They 

 are almost certainly of Tertiary age, so that the term " diabase " is not used here 

 in its strict signification, but is applied in this case to a decomposed rock of dolerite 

 affinities. They are sometimes somewhat acid in character, but at other times they 

 contain much granular augite. The porphyritic dykes occasionally approach augite- 

 camptonites in character, with violet-coloured augite and very rarely with hornblende 



* " Uber Basalte der Aucklands Inseln," by Max Hartmann : L.J., 1878. 



f G. T. Prior, Nat. Antarct. Exped., Geology, p. 109. Note.^I have not seen the paper on 

 the subject in the Mineralogical Mag. (1899) by the same author. 



