168 GLACIAL ACTION IN TASMANIA. 
basaltic eruptions which closed the latter, the land appears to. 
have risen again gradually, and the paleogene sediments have 
been deeply cut into. The terraced gravels of the Ringarooma 
Valles and North-eastern Tasmania generally, show that the 
elevation has been practically continuous, though on the 
islands in Bass Straits there are proofs of minor oscillations 
of level, hence we must conclude that the general elevation of 
the country is now higher than it has been since the early 
part of the paleogene period. It has not risen quite so high 
as previous to the great subsidence, for we find deep leads at 
Beaconsfield and George’s Bay running considerably below 
sea level (270 feet at Beaconsfield), and the old channel of 
the Ringarooma River at Derby is more than 90 feet lower 
than the present one. No elevation of the country sufficient 
to cause its glaciation has therefore occurred since the 
beginning, probably, of the miocene period. 
The second great cause of accumulation of ice is found in 
geographical changes leading to a redistribution of sea and 
land, alteration of ocean currents, and change in the direc- 
tion of prevalent winds. The most important change which 
would be likely to affect Tasmania in this respect would be the . 
opening of Bass Strait, and the severance of this island from 
the Continent. The biological proof is conclusive that there 
was practically unbroken laid connection between us and the 
mainland up to early in the pleiocene period, and if the glacia- 
tion had taken place before the severance, it would be easy 
to suppose that the opening of the strait had led to an 
amelioration of climate, but as it appears to have been later: 
than this, it is hard to conceive any reason for formation of 
glaciers which would nct exist now as well. In the neogene 
and recent period, too, we have no evidence of changes 
in the Australian Continent which could bave any effect upon 
our climate, and consequently we have to abandon this 
explanation also. 
It is therefore probable that the refrigeration of the 
climate of Tasmania, which led to the gathering of glaciers 
on its high mountains, was due to the causes insisted upon by 
Dr. Croll.and Sir Robert Ball. It is most likely true that these 
causes are not, of themselves, sufficient to account for a period 
of extreme glaciation such as was experienced in the Northern 
Hemisphere in the glacial period without the concurrence of 
geographical changes favourable to its production, but never- 
theless the astronomical and physical argunient is so strong 
that we must concede that it would account for a very con- 
siderable refrigeration. 
In discussing the subject of the climate of this colony 
during the neogene period, Mr. R. M. Johnston considers 
that there is no evidence of glacial action in the lower lying 
lands, and regards the giaciers as having been of small 
