688 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



[Geology. 



origin. The limestone, in particular, is traversed in all directions by vertical and 

 horizontal intrusions, which on the western cliffs form a complete network. They 

 vary in composition from trachyte to basalt. One igneous rock is of special interest. 

 It is found at an elevation of 400 ft. on the north-east slopes of Mount Dumas, nep.r 

 the western shores of Perseverance Harbour. In composition it is a porphyry, but 

 contains a notable amount of zircon in relatively large crystals. Finally, a covering 

 of peat, 40 ft. thick in the valleys, though only 10 ft. thick on the sloping ground, 

 and practically absent from the hill-tops, is still of sufficient importance to mask 

 all the surface features. 



In this brief statement of the rock-occurrences it will be noticed that there are 

 important differences from the account given by Filhol. As mentioned earlier, no 

 trace of mica-schist in situ could be found by the members of the expedition. 

 The granite mentioned 

 by Filhol as occurring in 

 a dyke in the schist de- 

 scribed by him at North- 

 west Bay could not be 

 found. Though this 

 granite is stated to occur 

 at the tide -level only, it 

 was expected to be con- 

 spicuous, for Filhol men- 

 tions large crystals of 

 mica as distinct. On the 

 other hand, Filhol makes 

 no mention of the large 

 mass of gabbro which 

 actually forms the west- 

 ern side of the bay. It 

 is hardly possible that 

 Filhol mistook this rock 

 for granite, but he gives 

 no accurate description of the rock which he calls granite. 



As will be mentioned in detail afterwards, the volcanic rocks collected by the 

 members of the expedition were in several important respects wholly different from 

 those described by Filhol. 



Geological History. 



The oldest rock found in Campbell Island by the members of the present ex- 

 pedition is the mass of gabbro near the south-west corner of the island. Reasons 

 for considering it older than the sedimentary and volcanic materials have already 

 been given. The absence of pebbles of gabbro in the Miocene sediment, however, 

 is remarkable. It must also be remembered that in Mount Menhir the gabbro 

 now rises above the Miocene sediments. The uneven nature of the surface of this 

 mass is believed to be sufficient to prove that land existed here before Miocene 

 times. This conclusion is supported by the observation of the nature of the lowest 

 Miocene sediments. It will be remembered that they consist of gravels and 



Fig. 6. — A Sill of Basalt, Nokth-west Bay, Campbell Island. 



