328 Transactions. 



rocks it will be most convenient to refer in sequence to the various locali- 

 ties whence specimens have been obtained, and these will be taken in order, 

 going round the coast in a general clockwise direction, starting from Emily 

 Bay (see map, p. 323). 



Headstone, Hundred Acres. 



The two specimens from here may be taken as typical of many of the 

 rocks of the group. In the hand-specimen they are of dark-greyish colour, 

 vesicular, somewhat coarse-grained basalts, with numerous weathered 

 olivmes clearly visible. The specific-gravity determinations are unsatis- 

 factory, owing to their vesicular nature, but the value given by one rock 

 was 2-60, and the other 2-50. 



Under the microscope both rocks appear to be alike, and are somewhat 

 weathered. They are doleritic in character, and of an even-grained texture. 

 The constituent minerals are plagioclase (medium labradorite) in broad 

 laths, augite sometimes ophitically intergrown with the feldspar, but 

 usually in grains ; magnetite and other iron ores ; but the most important 

 constituent appears to be the olivine, which occurs in grains up to 1-5 mm. 

 in diameter, and much stained with brown hematite as a decomposition- 

 product ; occasionally, however, it is perfectly clear. 



BuMBORA Bay, South Side of the Island. 



Three specimens were obtained from this locality. All are dolerites 

 of dark-grey colour, slightly vesicular, and with numerous small olivines 

 visible to the eye ; specific gravity = 2-86. In section they are formed 

 of broad laths of plagioclase (labradorite) ; faintish-green augite with high 

 extinction angle, ophitically intergrown with the plagioclase ; large olivines 

 up to 1 mm. in diameter, edged and seamed with brown iimonite, some 

 crystals being idiomorphic ; titaniferoiis magnetite in grains, laths, and 

 broken-comb forms. Two of the specimens are much stained by chloritic 

 matter derived from the augite, these rocks being decidedly diabasic in 

 character. 



Included in the collection from this locality is a piece of pumice, but 

 it is in all probability of drift origin, as it is much wave-worn, and differs 

 mineralogically from the other rocks of the island. 



Anson Bay, North-west of the Island. 



The sequence of rocks in this locality appears to be as follows : The 

 underlying bed consists of scoriaceous basalt, and then come beds of 

 stratified tuff, which are succeeded by a coarse basalt exhibiting well- 

 marked columnar structure. 



The rock from the lowest bed is dark grey in the hand-specimen, very 

 scoriaceous, with the cavities partly filled- with a yellowish-green substance. 

 Under the microscope it appears to be a somewhat coarse-grained dolerite, 

 the feldspars (med. labradorite) are in larger size than is usual with other 

 rocks of similar species from the islands ; the olivines are occasionally 

 serpentinized, but sometimes quite clear ; the augite is much altered, and 

 passes into a green chloritic material which colours a great part of the 

 section ; and there is much secondary magnetite and Iimonite. This rock 

 appears to be of a less basic type than the remaining specimens, and more 

 diabasic in character. 



The tuffs, which according to Mr. Laing are distinctly stratified, are of 

 two kinds — the lower is a coarse tufi of reddish tint composed of fragments 



