58 
position of rocks, and by constant reference to authorities 
he can place each one in its proper place. 
From Tambo to Parslow’s we passed over a large area 
in which thousands of feet of rocks, originally deposited 
as sedimentary beds, and appearing in many parts as 
sandstones and mudstones, were in other places metamor¬ 
phosed, becoming first indurated with more or less of 
hydrous magnesian silicates in the planes of bedding or 
cleavage, then schistose, and finally passing into granitoid 
rock and granite. Again, we noted vast masses con¬ 
taining abundance of magnesia-mica, the whole indi¬ 
cating changes—mechanical and chemical—which must 
have taken place when these rocks were subject to great 
heat and pressure. That there should be so much feld¬ 
spar and mica in the altered rocks is no matter for sur¬ 
prise when the mineralogical character of the typical 
lower silurian rocks is considered. They are not, as a 
rule, very silicious, but rather argillaceous. 
The volcanic rocks met with between Parslow’s and 
Mount Ilotham are of singular interest. We saw no 
signs anywhere of any crater or cone. All that remains 
is a capping here and there on lower silurian rocks, with 
some thickness of auriferous gravel between the volcanic 
rock and the upturned edges of the Silurians. The sources 
whence the lava flowed appear to have been obliterated 
by the denuding forces at all times active in these lofty 
regions. 
At what time within the recent tertiary period was this 
lava erupted ? Is there any connection between it and 
the lava flows of the western plains ? And what was the 
physical geography of the country when the volcanoes 
that gave forth streams of lava over the once great plains, 
