719 
and minute specks o£ a black mineral — probably hornblende — can be recognised. 
Throughout the whole mass, the rock retains very much the same character. The 
mountain rises perpendicularly from the alluvial flat on the north bank of St. Helen s 
Creek, and in Barron Creek the mass is seen to be intrusive through an ‘ orthoclase 
porphyry ’ upon which the sedimentary strata arc seen to rest. No perceptible amount 
of alteration was detected in any of the sections in w^hich its intrusive character was 
observed.” 
BASALT. 
No. 2. GrooBEiv^oTiGn Island, MoBESBr Strait (New Guinea). 
'Sir W. Maegregor’s Collection. 
Section. — Vesicular, with minute augite and felspar crystals visible to the naked 
eye. Augite crystals are jdentiful, with glass and magnetite inclusions. Mr, Maitland, 
w’ho has recently visited New Guinea, suggests that the augite may have to be referred 
to enstatite ; in which case the rock would be classed among the andesites. The sauidiue 
crystals show growth by accretion in a very beautiFul maunci’. The ground-mass is so 
opaque that minute plagioclase crystals not thick enough to reach through and touch 
each surface of the section do not appear by transmitted light at all, while by reflected 
light a very large number of these minute pellucid crystals can be observed. 
No. 173. Palm Island. 
H. C. McDonald’s Collection. Sp. Gr. 2 622. 
Colour, speckled greenish-brown. The specks are yellowish. The rock has a 
compact texture.* 
Section . — This rock i.s so much decomposed that its section does not reveal very 
much. Its constituent miner<als are augite and felspar. Apatite (in considerable 
quantities) and magnetite occur as accessory minerals. 
The augite is much cleaved and shattered, the basal sections having very well- 
marked cleavage, parallel to 1 iO. 
The felspars must once have been of great beauty (and tbeir even size and 
perfect twinning is still discernible). They are associated with a green mineral of 
secondary origin, probably chlorite, plentiful, not regular in outline, not pleochroic, 
differences of absorption nil, between crossed nicols appearing a speckled yellow-green ; 
the specks do not extinguish uniformly. 
No. 15. Normandy Eeefs, Cooktown (Queensland). 
P. Bauer’s Collection. Sp. Gr. 2'808. 
Colour, black, with reddish spots. Compact, slightly vitreous, fine-grained. 
Section. — Ground-mass abundant, with idiomorphic hyalosiderite, or perhaps 
fayalite, and plentiful hydrous oxide of iron, pseudomorphous after olivine. The latter 
mineral exhibits all the stages of decomposition, some examples being quite fresh and 
coffin-shaped, others having a deep-red margin and clear interior, others being only 
specks, and others being tvithout a trace of the original olivine. The olivines are the 
only crystals of any size in the rock ; they measure from 04 inch to ’06 inch in length. 
The rough look, owing to a high index of refraction, is marked. In one or two rare 
cases the red envelope round an olivine is packed with magnetite. There are no 
inclusions. The drawing on Plate XIX. of Eoscnbiisch’s “ Physiography of the Hock- 
making Minerals” illustrates these olivines exactly. The ground-mass is peppered 
■* Mr. McDonald stated that this sample was taken from a dyke passing through a “conglomerate” 
dipping towards the sea. 
