718 
so changed as to be impossible to identify. Another remnant of what has been a large 
prism, measuring .'OS inch by '01 inch, is crossed by yellowish-red bars of a non-fibrous 
but rather granular structure, feebly anisotropic. If Ibis crystal could be re.stored and 
identified, great light would be thrown on the whole matter of the origin and life-history 
of this rock. Asa concluding observation, the proximity of cnlcite to the relics of this 
crystal audits possible occlusion amongst the somewhat heterogeneous nias.s of secondary 
mineral matter is to be noted. 
(10) Sexfoetii Hills, West Side, Mackax. Sp. Gr. 2'4S. 
Colour, dirty grey, with a tinge of blue. Quartz is the only porphyritic mineral, 
and is embedded in a fine-grained pasty-looking ground-mass. The whole rock is 
sjirinkled with fine blackish grains. The quartzes are very brilliant. 
Section. By reflected light, the ground-mass consists of kaolinized felsjiars, not 
lath-like, but granular and pretty uniform. The black grains are innumerable, not 
shai ]), but ii regular, and otten surrounded by ferrite. Under the ^-inch objective the 
fresh felspars are twinned, and might be orthoclase or saiiidine. Owing to dusty matter 
and kaolinization, it is difficult to identify these very minute felspars, particularly as 
they are too small to be inspected under any lower jiower than the i-inch. There is no 
interstitial glass or fluxion-structure. Quartz is the only porphyritic mineral, and is 
rounded, showing, in two or three cases, the “ bays, inlets, and islands ” peculiar to the 
quartzes of the rhyolites and porphyrites. The quartzes carry liquid, gaseous, and 
glassy inclusions. Mr. Maitland says : — 
Near the head of Niddoe’s Creek, one of the watercourses draining the 
western side of that range of hills lying between the Main Eange and the Coast, a 
trachyte lava of a somewhat different character is seen dipping soiith-eastat an angle of 12 
degrees, and resting upon the sedimentary rocks of which this range is made up. 
Lithologically the rock may be called a quartz- trachyte, and throughout it presents a 
great nnifoimity in its physical characters ; it is made up of a light-grey, porous matrix, 
in which quartz, sanidine, and small specks of what appear to be hornblende are 
embedded.” 
(11) The PrNXACLE, Saint Helens. 
A nearly white rock, weathering red, very fine in grain, and without any 
porphyritic minerals. 
Section. By reflected light. Fine-grained, without any porphyritic minerals, 
with a few green and much corroded fragments and many minute specks of a reddish 
semi -translucent hydrated oxide of iron. The base is microlitic, without any pasty 
matter whatever, and is built up of orthoclase, plagioclase, and quartz, and tlie greenish 
mineral may be mica very much corroded. Mr. Maitland says ; — 
“ In the Parish of St. IIolous, on the south bank of Alligator Creek, a lofty 
I'idge of mountains, the 1 lunacies, which form a corry, cncircliug one of the branches 
of this creek, a great thickness of lava occurs. The rocks are traehyte.s of a brownish- 
grey colour, and with which fine-grained trachyte tuffs are aasociatcL The lava-4ieets 
have their steeper faces soutluvarJs, and appear lo dip in a general northerly direction. 
One of the sources from which some of these lavas and ashes have been ejected appears 
to be Mount Barron, a steep, triple-peaked mountain, the highest suinmit of wdiich is 
about 2,000 feet above sea-level, and which is almost surrounded by the head-W'ater,s of 
St. Hcien s Creek. (Section I\.)- The rock of which this mass is made up is greyish- 
white in colour, and somewhat porous, with a mean specific gravity, as determined by a 
Walker’s Specifia Gravity Balance, of 2 m. In the matrix, small crystals of sanidine 
