30 A. W. HOWITLT ON THE PHYSICAL GEOGRAPHY AND 
beds are more or less coarse conglomerates, sandstones, sandy or 
slaty shales, all of a reddish or yellowish colour, and narrowly re- 
sembling similar beds in the Iguana-Creek series. We have also here 
a great thickness of felstones, in which occur not only the wavy un- 
dulating lines of various colour, but also the angular fragments of 
different colour and texture such as are seen so frequently in the 
ash and fine agglomerates of the Wombargo Mountain and other 
localities of the Snowy-River porphyries. 
Near the summit the Snowy Bluff is encircled by a high precipice. 
The rugged face is worn into cavernous hollows as the component 
rock varies in hardness, and is seamed in all directions by a multi- 
tude of joints. It is only to be ascended in a few places, where 
rain-gullies have cut through from the upper grassy slopes of the 
mountain; but elsewhere is the inaccessible haunt of the Rock Wal- 
laby. 
This series, some thousand or more feet in apparent thickness, 
consists of various beds of a basic igneous rock, either porphyritic 
with plagioclase prisms, as in the lowest bed visible, or dense in 
texture, or vesicular and amygdaloidal, as in the upper parts. But 
everywhere the joints are lined or filled by quartz, chaleedony, or 
yellowish-green epidote ; and the cavities are either geodes of quartz 
and epidote, or filled by those minerals severally or by chalcedony. 
An examination of this precipice and of its various component por- 
tions, as well as of the underlying and overlying strata, has led me 
to conclude that these basic igneous rocks are interbedded, and not 
intrusive. 
A preliminary examination of some thin sections of these rocks 
which I have prepared for the microscope at once disclosed to me 
the familiar appearance of close-grained dolerite or basalt, in which 
either the plagioclase or the magnetite were predominant, and in 
which quartz, chalcedony, and epidote have been very largely intro- 
duced as secondary minerals. The plagioclase has in many cases 
been altered from the centre outwards by (apparently) chloritic 
minerals, and the magnetite has become still further oxidized, so as 
to show the translucent blood-red colour of hematite. 
In accordance with the views which appear now to meet with 
general acceptance*, these rocks, as being probably dolerites or 
basalts of pretertiary age, would be classed under the restricted term 
of Melaphyre, or perhaps they may with still greater propriety be 
called Upper Devonian Dolerites. 
In a paper which I am preparing for the next Progress Report of 
the Geological Survey of Victoria I hope to be able to describe more 
fully the microscopic as well as the macroscopic peculiarities of 
these most interesting rock masses. 
In proceeding to the eastward of the Mitchell River no traces of 
* Zirkel, ‘Untersuchungen, &e., der Basaltgesteine,’ p. 198: Tschermak, 
‘Die Porphyrgesteine Oesterreichs,’ p. 136 ; Allport, “ Microscopic Structure and 
Composition of British Carboniferous Dolerites,” Quarterly Journal of the Geo- 
logical Society of London, 1874, vol. xxx. pp. 529, 530. Other references might 
be given, but these may suffice. 
