715 
MACKAY DISTEIOT. 
The following eleven roclts from tlie Maekay Disti’ict, together with the very 
excellent sections thereof, were kindly lent me by Mr. A. Gr. Maitland. They are, 
without exception, the thinnest sections described in this Paper, having been sliced in 
London by Mr. Cuttell, of Kentish Town. Drawings and sections showing the mode of 
occurrence of the rocks in question, given in Blr. Maitland’s “ Report on the Geological 
Features and Mineral Resources of the Maekay District,” * are reproduced in Plate 4(3, 
figs. 1 and 2, of this Work. 
(1) Feom a Gap oh the Nobth side of Mount Jukes. Sp. Gr. 2’490. 
Colour, red, blotched with white specks. 
Section . — Shows granulitic quartz, the grains about '01 inch ; comparatively very 
large orthoclaso, as Carlsbad twins, the largest reiiching ’08 inch in length. These felspars 
are dusty with ferrite, which gives the rode its colour. They are all kaolinized, and but 
for the exceeding thinness of the section could not be identified. No plagioclase. A 
few crystal wrecks with grains polarising in high colours on the margin of holes 
originally occupied by a primary crystal. These grains have a clean bright aspect in 
ordinary light and might be epidote or olivine. A good deal of opaque oxide of iron 
incysts these brilliant specks. Under the -j-inch objective, the quartzes have a few 
inclusions : some may be glassy, others are certainly fluid with moving bubbles. (FiWe 
Mr. Maitland’s “ Report” and Section on PI. 4(3, fig. 1.) 
(2) Mount Mahtin, Joiijiont Creek. Sp. Gr. 2-570. 
Colour, dirty brown. Fine-grained. The hand specimen looks like a felsite. 
There are no porphyritic crystals. 
Section. — Ground-mass a felt of microlites, without any glass, but between crossed 
nicols feebly illuminated. Felspars much changed, packed with granules, which are the 
only points of illumination thi-oughout, the rest of the section being a dark-lavender 
colour. The granules may be epidote. Orthoclase was a constituent mineral of the 
rock. Magnetite (or titanic iron), with a little apatite, is present in small quantity, but 
at fairly wide regular intervals. One hexagonal section of the latter measures about 
'10 inch. 
(3) Mount Mandakana, “ The Leap.” Sp. Gr. 2-498. 
A white rock, speckled with small black grains and sanidine ; highly porous 
when applied to the tongue. 
Section . — The ground-mass is made up of a little granular quartz and numerous 
felspar laths, and is holocrystalline. The macroscopic sanidine (Carlsbad twins) is 
perfectly limpid and show-s the faulting along the suture, the boundai-ies not participating 
in the apparent movement, as pointed out by Rntley.-f- Under the i-inch objective, 
the black specks turn out to be grains of deep-green mineral, with marked differences 
of absorption when viewed with polarizing prism. With these specks, apatite, and 
perhaps magnetite, is associated in fine grains. No fluxion-structure. In the felspars 
of the ground- mass ks one beautiful spherulite, the arms measuring nearly -03 inch, 
but I cannot find another in the whole section, which is seven-eighths of an inch in 
diameter. Mr. Maitland says : — 
“ One of the most conspicuous examples of the lavas is to be found at Mount 
Mandarana, better known as the Black Gin’s Leap, close to the Bowen Road, about twelve 
miles north-west of Maekay, w-here it forms a broad table-like mass, rising to a height 
* Brisbane : by Authority : 1889. 
t F. Rutley. The Study of Rooks, iii. Edition, page 44. 
