32 A. W. HOWITI ON THE PHYSICAL GEOGRAPHY AND 
apparent ; and I incline to the belief that they belong to the age of 
the latter, that is, that they are Upper Devonian. Their position 
as regards the Middle Devonian limestone of Bindi favours this view. 
Further again to the eastward numerous traces of ancient con- 
glomerate beds are met with resting on the summits of the mountains, 
as, for instance, near Carrabungla, at the sources of the Limestone, 
Tambo, and Reedy Rivers, on the flanks of the Cobboras near 
Cowombut, and again further to the south and east at Combyingbar, 
near the boundary-line of this colony. ‘These are similar to those 
with which the groups at Mount Tambo and the Snowy Bluff com- 
mence, and may, with much probability of truth, be regarded as 
parts of the Great Upper Paleozoic arch, of which the Iguana-Creek 
beds seem to be the lowest. 
According to an opinion expressed to me by Professor M‘Coy he 
regards the marine limestones and shales of the Native-Dog Creek and 
Cowombut as somewhat older than the Iguana-Creek beds, and this 
would accord very well with the facts I have observed in the field ; 
for at the former places the last traces of these marine beds are 
found to be resting on the Snowy-River porphyries in the bottoms 
of basins, while high up on the intervening mountains (the Cobbo- 
ras) are the old conglomerates of which I have spoken. 
It will have been remarked that almost invariably the Buchan 
and Bindi Limestones, wherever met with, are seen to lie in basins 
of the older rocks. ‘The same peculiar feature is to be remarked in 
the Upper Devonian limestones and calcareous shales of the Native- 
Dog Creek and of Cowombut, and in the Mount-Tambo and Snowy- 
Bluff beds. The explanation is afforded by the section at Mount 
Tambo and by a view of the north side of the Snowy Bluff. 
We there see that the preservation of these beds is due to the 
circumstance that in the folding of the earth’s crust, after the laying 
down of the Devonian strata, certain portions formed what may be 
termed ‘‘ pockets” in the lower “ paleeozoic formation.” Subsequent 
denudation left these ‘“ pockets” below the general surface, and 
erosion by the rivers has worn them out into basins by the removal 
of the limestones and shales more rapidly than the refractory and 
silicified rock masses in which they generally rest. In Mount 
Tambo and the Snowy Bluff we may see the converse of the process 
which I have indicated as having taken place in regard to the De- 
yonian limestones. In those instances the synclinal ‘“ pockets ” 
consisted of siliceous rocks which have proved harder to remove than 
the older formations in which they were enfolded. 
3. Carboniferous. 
(g) Avon Sandstones.—Of this group of strata [I am at present 
able to say but little. Mr. A. R. C. Selwyn, in the ‘“ Notes on the 
Physical Geography, Geology, and Mineralogy of Victoria,” Exbibi- 
tion Essays, 1866, speaks of them as being “ yellow and brownish 
red coarse-grained sandstones and micaceous freestones with nume- 
rous impressions of plants. Very good specimens of Lepidodendian 
