Physiography, Geology.] SUBANTARCTIC ISLANDS OF NEW ZEALAND. 731 



face of one of these fiat extensive flows, Tlie liill-tops, too, sliow tlie effects of tliis 

 horizontal character. They are very frequently almost flat over wide areas, so that 

 distinct peaks are exceptional (fig. 12). AVhen their edges are exposed on the 

 sea-shore, or round the heads of valleys, columnar structure is exhibited in its most 

 perfect form. The south shore of Enderby Island (fig. 13) and the head of Cole- 

 ridge Bay and Musgrave Harbour afford splendid examples of this structure. 



The lava-flows are cut by a series of dykes which are of basic character — 

 viz., diabases, and basic porphyrites approaching augite-camptonites. None of these 

 were observed cutting the higher flows, although the hill-tops were easily and 

 extensively examined, but dykes were frequently seen on the shore. They ma)^ 

 extend upward for some distance, as the thick covering of scrub and tussock and 

 peat completely masks the surface for nearly 1,500 ft. 



Petrology of the Carnley Basalts. 



In order to determine, if possible, the sequence of the flows, specimens were 

 taken from all exposures up a ridge from sea-level to the summit, both at Adams 

 Island and at the head of North Arm. Unfortunately , these are necessarily very im- 

 perfect, owing to the surface being hidden by a close plant covering. In order to give 

 a clear idea of the sequence, a description is given of each specimen taken ; but it 

 must be remembered that these are from flows exposed on the shore, and then with 

 a great hiatus — from those exposed for the upper 300 ft. or 400 ft. or more. Thus 

 the middle and lower portions are unrepresented. Again, difference in texture 

 of the rocks may be due to the position from which specimens were gathered from 

 a flow : those taken from the middle would, in general, be coarser than those from 

 the edge. 



ADAMS ISLAND SERIES. 



No. 1. Hornblende Basalt. 



Macroscopic. — A dense rock, very fine grained ; only an occasional feldspar 

 phenocryst present. 



Microscopic. — The groundmass is fine - grained, with occasional portions of 

 slightly coarser grain. It is partly glassy, and contains small laths and microlites 

 of oligoclase-andesine, simple or once twinned, scattered grains of magnetite, and 

 a good deal of secondary chlorite derived from hornblende. There are occasional 

 fresh twinned plates of plagioclase between oligoclase and andesine, and small grains 

 of brown hornblende. 



Note. — This is here the lowest member of the basic series which is exposed, 

 and is very like a rock lying immediately over the conglomerate at Camp Cove. 



No. 2. Basalt. 



Macroscopic. — A black fine-grained rock, with small phenocrysts of feldspar 

 and, in lesser proportion, augite. 



Microscopic. — The groundmass shows a slight flow structure, and is especially 

 fine-grained in the neighbourhood of phenocrysts. It contains a large proportion 

 of feldspar laths, a good deal of violet augite and magnetite, and a little brown 

 hornblende. An occasional large grain of augite occurs, but the dominant pheno- 

 cryst is andesine-feldspar in fresh squares and elongated plates. 



