36 A. W. HOWITT ON THE PHYSICAL GEOGRAPHY AND 
They are not only scarped at the sides, but occasionally completely 
isolated by the sources of streams feeding the adjoining rivers. 
There is, for instance, evidence pointing to the conclusion that the 
Dargo and Cobungra High Plains were onee continuous across the 
present valleys of those rivers. This is shown by the Tabletop 
Mountain, which stands in the valley of the Upper Dargo River. 
Underneath these flows is found in places auriferous quartz-gravel, 
which is now worked by miners. ‘The deposits have not yet been 
sufficiently opened up to admit of any opinion being formed as to 
their precise nature or value; but there is little doubt that they will 
prove to be the ancient beds of those streams which now flow in the 
valleys a thousand feet or more below. 
At Cobungra layers of black clay have been met with in the auri- 
ferous quartz-gravel, and contain lignite and leaf-impressions ; but 
these have not yet been determined. 
I have nowhere observed the traces of volcanic orifices. It is 
possible that craters may have been situated in those tracts now 
eroded into valleys; but, on the other hand, itis somewhat improbable 
that all volcanic orifices connected with the various lava-flows spread 
over such a wide district should have been obliterated, or that, if such 
existed in the areas now seen as valleys, some traces of them 
should not have remained. During ten years that I have been con- 
stantly looking for such evidence I have never met with it. Mount 
Battery on the Cobungra River certainly appears at first sight to 
resemble a voleanic cone; but on inspection it will be found that it 
is merely a projecting spur from the doleritic sheet of the Cobungra 
River. In places a well-marked columnar structure is seen, vertical 
to the horizontal flow; and I have no doubt that it is merely a much 
thicker portion of the sheet which has filled the former valley, and 
has been subsequently isolated by the river. 
Throughout the whole of the district in which these volcanic rocks 
occur, and which extends only about thirty miles south of the central 
chain, immense numbers of intrusive dykes and masses of basic 
igneous rocks are met with. An inspection of thin slices from a 
great number of these, from all parts of this district, has shown me 
that a large proportion exhibit the familiar appearance of doleritic 
and basaltic rocks, and, moreover, of exactly the same general mineral 
character as the Tertiary dolerites and basalts of the district. These 
are characterized by a predominance of plagioclase and magnetite. 
It seems therefore not impossible that these great doleritic and 
basaltic flows have been emitted from fissures rather than from true 
volcanic orifices. 
It seems worthy of remark that we should find these traces of 
Tertiary volcanic activity following the direction of the Great Dividing 
Range. So far as I am aware, they extend in the same way far into 
New South Wales. 
Gold- Workings. 
I have not touched upon the gold-workings of the district: the 
subject is hardly within the scope or the limits which I had proposed 
