BY A. MONTGOMERY, M.A. 167 
between the paleogene and neogene periods, or probably 
pleiocene; and this would make the glacial action either 
pleiocene or post-pleiocene. Not having direct proof of glacia- 
tion at Mount Bischoff, this argument is not convincing, but 
taken in conjunction with the fact next to be mentioned, it 
has weight. On Gads Hill, and at various points along the 
top of the Oakley Range, the same tertiary basalt is found as 
a superficial covering, and an escarpment of it forms the 
western edge of the plateaux on the top of the Oakley Range 
and overlooking the River Forth. The valley of the Forth 
has plainly been scooped out since the basalt was poured 
out, and as we have seen, at the head of this valley, the 
proofs of the presence of glaciers are very well marked. 
Consequently the pleiocene or later age of the glaciation must 
be regarded as demonstrated. It may here be remarked 
that, according to Dr. von Lenderfeld, the evidences of glacial 
action in the Australian Alps point to its having taken place 
at quite a recent date, and with this corroboration I think 
that it is most likely that our glaciers existed as late as the 
pleistocene period. As above stated, the excellent preserva- 
_tion of the rock surfaces, the slight decomposition of the 
greenstone erratics, and the small amount of erosion of the 
ground moraine at Barn Bluff, all go to show a very recent 
date, geologically speaking. 
The importance of being able to limit the probable period of 
existence of the glaciers to neogene and recent periods becomes 
apparent when we come to consider the questions of the 
cause and extent of the glaciation of the country, and as to 
whether our cold period had any connection with the glacial 
period of the Northern Hemisphere. First let us glance at 
the causes of glaciation: It might be due to greater elevation 
of the land, to geographical changes resulting in a redistri- 
bution of sea and land, diversion of ocean currents, and so on, 
or it might be due to astronomical, causes as so lucidl 
explained by Sir Robert Ball in his recently-published little 
book on ‘‘ The Cause of an Ice Age.” Having limited the 
period of existence of the glaciers to the time between the 
outpouring of the basalts and the present day, we can 
examine the evidence of our later tertiary deposits to 
find if there is any indication of the country having 
subsided from a higher elevation to a lower one. We 
find that all round the island, in the Launceston ter- 
tiary basin, in that of the Derwent, at Macquarie Har- 
bour, and at Oyster Bay, there are palacogene lacustrine 
deposits laid down in hollows, the bottoms of which are often 
much below present sea level, and which are in the Launceston 
Basin as much as 1,000 feet in thickness. They have doubt- 
less been formed during a period of continuous subsidence 
extending throughout the paleogene period. After the 
