726 
No. 13. Day Dawn P.C., Chaetees Towees (Queensland). 
A. W. Clarke’s Collection. Sp. Glr. 2'f)4‘9. 
This sample of rock comes from the No, 10 level, and is almost black in colour, 
very fine in grain. 
Section . — Hornblende is the prevailing mineral. With ordinary light, it is in very 
slender long needles which are felted together. The felspars are plagloclase, and not 
clear as in the last example of diorite. No quartz, and but little magnetite. 
No. 17. Quaeet Beseete, Mount Al^ia, Chaetees Towees (Queensland). 
A. W. Clarke’s Collection. Sp. Gr. 3 057. 
Colour as in No. 13. 
This is a very similar diorite to No. 13, being of interest only because the 
diorite No. 13 is from a depth of about seven hundred feet, while this is a surface rock 
distant about one mile from the mine. 
PORPHYRITES. 
Nos. 129 TO 151. Cbotdon (Queensland). 
Sp, Gr. : Mean, 2'512 ; Extremes, 2'396 and 2-610. 
In the following description a good deal of ground is covered ; the notes being 
culled from some twenty-three rock samples collected by Mr. Jack. At one end of the 
series, the rock is jet-black, very compact, with conchoidal fracture, and studded with 
quartz whose surface of fracture is coincident with that of its matrix. At the other end 
of the series, the rock is milk-white with identically similar quartz. The rock occasionally 
shows blebs of graphite, and about the middle of the series the hand specimens appear 
banded with different coloured varieties of the same rock. The larger quartz grains 
cause waves in the banding, just as in sections of the rhyolites. 
The following notes on the microscopic sections do not throw much light on 
these roulta, and the whole matter is in the hands of the Geological Survey Department, 
but they form an item of information which may not be devoid of interest : — 
Ground-mass under the 2-ineli objective shows no interstitial glass, and polarizes in 
a hazy way, but every illuminated speck suffers extinction in the course of revolution of 
the stage. Perfectly opaque, amorphous patches of a white substance (not unlike kaolin) 
are distributed over the slice. By refl.ected light these patches are seen to aggregate 
together. Part of the ground-mass is eoarsf r in its crystalline structure than are other 
portions, and the quartzes are all more or less penetrated by it in the shape of bays, 
inlets, and islands. The isolated ground-mass in the quartzes is due probably to the 
transverse sectioning of a penetrant tongue. There are the wrecks of orthoclase 
crystals. The ground-mass has so penetrated and become part and parcel of the original 
crystals that it is difficult to speak with certainty as to whether they were sanidine. 
In the quartzes are numerous glass-inclusions with fixed, and some few moving 
bubbles. There is a patch of faintly green granular particles mixed with the ground- 
mass. The green grains are very faintly dichroic (faint green to pale faint yellowish- 
green). The quartzes ai-e mostly rounded cn their edges and angles. 
In other sections the pale-green granular flecks are seen aggregated together 
in what appears like the wreck of a crystal. These flecks are faintly dichroic, and in 
one aggregate there is possibly apatite, but it is uncertain. The very small green 
grains are sometimes numerous, and, under the i-inch objective, allotriomorphic. They 
are not dichroic. 
Some patches of undoubted hornblende occur, which, though not very fibrous, 
are too much changed to allow me to speak certainly on this point. Black, opaque 
