CHAPTER XL. 
PETEOGEAPHICAL NOTES ON SPECIMENS FEOM QUEENSLAND 
AND ADJACENT COLONIES. 
BY A. W. CLAEXE, P.G.S. 
INTBODUCTOBT. 
When Die following Notes were being compiled I hoped that they would form 
portion of a larger work, viz. : — ^The description, in petrological language, of the rocks of 
Australia ; but want of time, together with the difficulty of getting typical rocks from 
the other colonies, has narrowed the scope of this ambitious attempt, so that little has 
really been done besides describing a few of the rocks of Queensland and the 
neighbouring Colonies. 
As a Queenslander (by adoption), I am glad to be able to contribute, in any way, 
to the codification of our natural history; and the appearance of these Notes in Messrs. 
Jack and Etheridge’s Work on the Geology and Palaeontology of Queensland is 
gratifying to me, and not inappropriate, since nearly every rock described in the 
following pages was collected by the Government Geologist, or by members of his Staff. 
For the last three years I have constantly been supplied with field notes and reports on 
these rocks, and am now entrusted with a great deal of the petrological work of the 
Geological Survey, so far as the preparation of rock-sections is concerned. 
The microscopical drawings, signed “ J. Phosbe Clarke,’ ’ were drawn and painted 
from the microscope by my wife. To those persons who know anything of the subject, 
they tell their own tale ; but for general readers it may here be necessary to describe, 
as shortly as possible, what they mean and teach. 
Imprimis, the drawings are made from the highly magnified images of extremely 
thin films of rock. Each film is preserved between two glasses, which are made to adhere 
together by means of Canada balsam. These films or sections show the exact relative 
positions of the different constituents of the rock. When they are placed under the 
microscope, and light is reflected from the sub-stage mirror through the section, the 
structure or texture of the rock is revealed, and this is a highly important factor in 
the grouping and classification of rocks. Thus the New Guinea rhyolite, No. 108, 
drawn on Plate 61, fig. 1, represents fluxion-structure, as do several other of the 
drawings appended to those Notes. 
In petrological language, “fluxion-structure” means that the section bears 
irrefutable internal evidence of flow during thar period of the existence of the rock 
when its temperature just allowed the creation out of the molten magma of one or two 
classes of minutely crystalline minerals, which thus become indices of the past move- 
ment of the rock. 
In examining this particular group of rocks it is easily seen that the microscope 
plays an important part ; for to the naked eye the little lath-shaped crystals seen in the 
magnified section are generally invisible, while the microscope discovers their presence 
and arrangement in vast numbers throughout the glas.sy base, resembling what occurs 
when a bundle of twigs and straws is cast into a running brook — viz., the twigs and 
straws arrange themselves end to end in the direction of the flow of the brook. 
Eocks whose sections reveal, microscopically, this end-to-end arrangement of lath- 
shaped crystals (crystallites) are placed in the rhyolite group. 
There are other rock structures or textures which are described in various text- 
books on the subject, and occasionally our own Australasian learned Societies deal with 
