696 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



[Geotogy. 



small microlites, which often show a flow- structure. The augite is of a pale-grey 

 colour, and is still more minute than the feldspar. It is associated with abundant 

 magnetite. The olivine is also in minute crystals, which do not occur very com- 

 monly, and are stained yellow owing to the formation of limonite. In each case 

 there is a coarse-grained lava below the fine basalt. This contains large crystals 

 of feldspar which is undoubtedly labradorite. The other minerals are in smaller 

 crystals. The olivine is much changed to serpentine, Augite is practically restricted 

 to the groundmass ; it is brownish. Magnetite and titaniferous magnetite are 



rather abundant. 



Analyses. 









Mount Honey, 



Beeman Hill 



near Summit. 



Basalt. 



SiOo 







53-40 



52-36 



Al.,03 







15-94 



14-20 



Fe.Og 







9-14 



5-80 



FeO 







3-59 



6-68 



CaO 







8-57 



7-40 



MgO 







3-37 



3-09 



TiOa 







2-60 



2-40 



Na,0 







2-18 



5-42 



K2O 







1-19 



2-06 



H2O 







1-51 



1-57 



100-39 



100-98 



Beeman Hill is composed of basalt of rather a different kind ; it is por- 

 phyritic, but augite as well as feldspar occurs among the larger crystals. In the 

 field occurrence this rock has a distinct columnar structure. 



The summit of Mount Paris is composed of a basalt that has a few porphyritic 

 crystals of labradorite, but the base of the rock is very fine, and the augite is 

 pale grey. 



At the top of St. Col Peak the basalt is rather similar to that at the top of 

 Mount Paris. 



Several of the dykes on the western shore of Perseverance Harbour are formed 

 of a basalt that is closely related to diabases in structure. These rocks do not 

 contain any olivine. They are very dense. The augite is in plates of small size, 

 but sometimes encloses a few feldspar microlites ophitically ; it has a violet 

 tint, which probably indicates that it is titaniferous. The feldspar is in the 

 form of microlites only. There is a good deal of glass and some serpentinous 

 matter. 



Several of the smaller dykes have a purely glassy selvage. The dykes on 

 the shore of Perseverance Harbour numbered 2, 14, 23, 24, 25, 4, 12, 9, and 22 

 are formed of this type of rock. 



Some of the basic rocks are coarse enough to call dolerites. Most of them, 

 such as that at Terror Point, are different from the basalts in texture only ; but 

 one, a light-grey rock, found near the summit of Lyall Pyramid, has porphyritic 

 crystals of olivine and augite. Dyke 7 is similar to it, as well as another dyke 

 on the west side of Mount Dumas. 



