Speight. — Petrolor/icaJ Notes on Eockx from ihe Ktrmadecs. 251 



the group, and the exact locality and position of the specimens are some- 

 what doubtful. I have classified these rocks into plutonic, dyke rocks, 

 lava-flows, and fragmentary deposits, without any regard to their age 

 relative to each other. 



Plutonic Rocks. 



Hornblende granite occurs as boulders in tuff or scattered on the surface 

 of the island. One block was fomid at an altitude of 1,600 ft. In the 

 hand-specimen this is a whitish even-grained rock, with light-coloured green 

 hornblendes of small size visible, as well as feldspar and a little quartz. 

 The specific gravity is 2-63. Under the microscope it is found to consist of 

 feldspar, both orthoclase and plagioclase (albite), the latter in large amount ; 

 quartz, irregularly distributed, full of liquid and gas bubbles ; epidote, 

 frequently developed along the cleavage-planes of feldspar ; apatite, in 

 grains and short needles ; and also titanite, which sometimes adopts the 

 wedge-shaped form so frequently characteristic of the mineral, and at others 

 occurs in aggregates. Neither biotite nor muscovite is present. From the 

 general character the rock shows a close relationship to a syenite, although 

 containing quartz. This rock appears to be similar to that described pre- 

 viously by Professor Thomas. 



Dyke Rocks. 



These rocks are found on the summit of Meyer Island and, as intrusions, 

 on the coast of Sunday Island. 



No. 8. Augite Andesite. — From a dyke on Meyer Island. 



In the hand-specimen this is a vesicular, dark-grey rock with prominent 

 feldspar phenocrysts ; its specific gravity is 2-56. It is an augite andesite 

 of the most acid type of the volcanic rocks examined. This is apparently 

 the rock described by Thomas in the " Transactions of the New Zealand 

 Institute," vol. xx, page 313. 



It is the only specimen received from the series of dykes mentioned by 

 Percy Smith (Trans. N.Z. Inst., vol. xx, p. 339) as intersecting Meyer Island. 



No. 29. Augite Andesite. — From a small sill or intrusion at Hutchinson 

 Bluff, Sunday Island. 



Macroscopic. — A fine-grained dark rock, slightly vesicular, containing 

 very small phenocrysts of feldspar. Specific gravity, 2-63. 



Microscopic. — The groundmass is fine-grained, contains much glass in 

 patches, with grains of magnetite and augite, and microlites of labradorite ; 

 there are very occasional phenocrysts of labradorite and augite. 



No. 30. Augite Andesite. — Occurs as an intrusion in tuffs on the north 

 coast of Sunday Island. 



This specimen is similar to No. 29, but is coarser in texture, and con- 

 tains much magnetite in grains. 



No. 40. Andesitic Basalt. — Occurs as a dyke in Scenery Bay, south 

 coast of Sunday Island. 



Macroscopic. — A grey rock, with prominent feldspar phenocrysts and 

 occasional olivines and augites. Specific gravity, 2-93. 



Microscopic. — The groundmass is composed of grains of augite and 

 olivines and plagioclase laths. In some parts there is a good deal of glass. 



