160 GLACIAL ACTION IN TASMANIA. 
_ sures; (2) a very similar coarse pebble conglomerate lying on 
the edges of older strata towards the south end of Mount 
Murchison. This one, I think, is older than the coal measures, 
and may be the Devonian conglomerate of Mr. Moore, but 
fossil evidence is not yet available to decide its age. And 38. 
A somewhat similar conglomerate conformably bedded with 
the quartzites and schists and intercalated in layers in them. 
This differs from the two former ones in being much more 
jointed, the joint planes passing fairly through the com- 
ponent pebbles, and in being also so thoroughly cemented 
together that when the rock is broken the pebbles do not 
break out from their setting but right across their sub- 
stance. he conglomerates of Mount Owen, Mount 
Zeehan, and parts of Mount Reid are of this third 
class, conformably bedded with slate and sandstone. I 
am not yet prepared to say that the quartzites and schists of 
the Upper Forth, and westward thence to Mount Murchison, 
are of the same age as the sandstones and slates of Mount 
Zeehan, though the included conglomerates among the 
quartzites are very similar to those among the sandstones of 
Mount Owen, but I have not seen any signs of uncomforma- 
bility up to the present, and the difference of lithological 
character may be due simply to the first named being nearer 
the axis of the mountain-making movement or crumpling. 
Nevertheless it seems rather more probable that the 
quartzites are older altogether than the Zeehan fossiliferous 
strata. The general strike of both formations, supposing 
them to be different, being the same, about N.N.W., and both 
lying inclined at high angles, it is likely to be a matter of 
difficulty to establish the fact of difference of age by strati- 
graphical evidence alone, and the paucity of fossils debars us 
from getting good paleontological proof. 
Mr. Moore mentions that Mount Sedgewick is capped with 
diabase greenstone, as is also Mount Dundas; to these we 
may add Barn Bluff, Mount Pelion, Mount Ossa, the Ducane 
Range, the Eidon Range, East Mount Pelion, and the Oakley 
Range, as all showing the same feature. It seems manifest 
to me that the great greenstone plateau in the centre of the 
island, the northern edge of which forms the Western Tiers, 
once extended westward so as to include all these peaks, and 
it is probable that ice action had a great deal to do with 
carving out the deep valleys that now separate them. I do 
not mean to say that ice has been the only considerable agent 
in cutting out the valleys, for these highlands do not appear 
to have ever been under water since the eruption of the green- 
Stones in mesozoic times, and great subaerial erosion must 
have taken place before the coming of the ice sheets, which, 
as we shall see later on, probably did not exist till a com- 
paratively recent time, later tertiary or even pleistocene. 
