Physiography, Geology.'] SUBANTARCTIC ISLANDS OF NEW ZEALAND. 721 



along the shore of Camp Cove and of the bay between it and Musgrave Harbour, 

 and are of such a size that they indicate the immediate neighbourhood of large 

 masses of the rock in position. Boulders of gabbro were found at Fairchild's 

 Garden, near the western entrance of Carnley Harbour, and on the beach on 

 the north side of Enderby Island, in such positions that they could not have 

 been carried far by any natural transporting agency. These boulders indicate 

 either the immediate neighbourhood of gabbro in position underneath these widely 

 separated parts of the island, or that they have been brought up from below as 

 inclusions in the more recent basalt. The former alternative appears to be the 

 more probable. These facts taken in conjunction with the occurrence of a 

 similar gabbro at Campbell Island, and of allied rocks (norites) at the Bluff, in 

 the extreme south of New Zealand, seem to indicate the existence of great intru- 

 sive masses of gabbro over wide areas. This intrusion is perhaps contemporaneous 

 with the intrusions of dunite and other basic rocks occurring on the western side 

 of the South Island of New Zealand, and passing through the centre of the Nelson 

 Province towards D'Urville Island, in Cook Strait. Such rocks also occur in New 

 Caledonia, with a connecting-link of norites found recently in the Auckland Penin- 

 sula, west of the Bay of Islands. They thus form part of a great convex arc facing 

 the Pacific Ocean, and enclosing the Tasman Sea area. As the intrusion occurs in 

 Lower Mesozoic rocks near Nelson, and it nowhere penetrates the Upper Cretaceous 

 beds in other parts of the country, it seems reasonable to assign its occurrence to 

 either the Jurassic or Lower Cretaceous period. It is probable that the intrusive 

 masses of the Auckland Island are of that date as well. It seems likely, too, that 

 they are connected with those movements which formed the Southern Alps and 

 brought about the severance of New Zealand from Australia, which no doubt occurred 

 in Jurassic or early Cretaceous times — a movement which in all probability was 

 intimately related with the formation of the Tasman Sea. 



The petrological character of the gabbro varies a good deal. In some cases 

 it is a dark rock with large crystals of pyroxene standing out on the weathered 

 surface. These frequently show the bronzy lustre of diallage on fracture. There 

 is also a finer-grained type of the rock, which is extremely tough and hard to break. 

 Under the microscope the rocks appears to be an olivine-gabbro with large crystals 

 of augite, which frequently show diallage structure. At times, especially in the 

 coarser variety, schiller structure is well developed ; the augite is slightly pleochroic 

 in purple tints. The olivine is in rounded grains, common in some sections and 

 almost absent in others, sometimes fresh, sometimes serpentinized, and, again, par- 

 tially replaced by magnetite aggregates. It is frequently completely included in 

 the augite plates as poecilitic grains. 



The feldspar is labradorite with the usual twinning ; the amount present varies 

 greatly. In the finer varieties it far exceeds the other minerals in importance, but 

 in the coarser type it is subordinate to them. It is usually fresh, in broad plates, 

 but occasionally it is broken up into a mosaic of small grains ; small fragments are 

 also included in the augite, in some cases with apparently definite orientation of 

 graphic intergrowths. Primary hornblende is a rare constituent, but a boulder 

 from Enderby Island contains a fair amount of both primary and secondary horn- 

 blende derived from the augite, and thus resembles somewhat the Bluff norite. It 

 is possible that this specimen has been brought from the Bluff as ballast for a sailing- 

 47— S. 



