102 THE GLACIER EPOCH OF AUSTRALASIA. 
epoch, and this denudation must have been in constant and 
intense operation ever since the upheaval of the plateau. 
Even if we allowed only a period of 24 millions of years to 
have elapsed between the upheaval of the great greenstone 
plateau, while allowing a waste at the average estimated 
rate of one foot of rock in 3,000 years, we must also allow 
that denudation, especially that powerful form of eating 
back against water courses, would have removed a 
quantity of matter—from its ravines especially—-equivalent to 
a uniform depth of 833 feet over its whole area; and this 
estimate in such an elevation is probably far too low. The 
denudation, which has been effected even since the earlier 
glacier epoch relatively, could not be a third of this amount; 
and since the maximum stage of the glacial epoch, 210,000 
years ago, probably not a tenth of the amount of denudation 
which must have been effected prion to the later glacial 
epoch. 
The probability that our valleys would originally eat 
inward in cuts against the vertical faces of the elevated 
plateau also invalidates any inferences drawn from the latest 
cuts made iu its watercourses far in the interior of the 
upland regions; for the beginnings or initial stage of a valley 
system at its original outer edge would give widely different 
results. However this may be, Mr. Montgomery’s observa- 
tions of recent actionare valuable, although some of the 
inferences drawn by him may not apply as widely as he may 
be inclined to consider at the present moment. In the 
greater number of conclusions formed by him, however, I 
cordially concur. The evidence given by him of glacial 
phenomena in the vicinity of Mount Pelion and Lake Hyre 
are particularly full and clear, and leave not the slightest 
doubt as to their genuine character. His demonstration of 
the existence of glaciers flowing from the elevated regions of 
Barn Bluff and Mount Pelion (whose peaks are fully 1,000 
feet higher than Mount Tyndall), of their discharge of 
moraine stuff, of their singularly perfect roches-moutonneés, 
and erratics at the 2,000 to 2,792 feet level near Lake Hyre, 
is simply complete and unassailable. His paper, as a whole, 
is the most comprehensive contribution which I have yet 
seen as regards the whole question of glaciation and its sup- 
posed cause, so far as Tasmania is concerned, I do not here 
refer to Mr. Montgomery’s views as to the causes of the 
glacial epoch further than to remark that he adopts in thé 
main the view which requires the concurrence of astronomical 
and favouring geographical and physical causes, a view which 
I myself have adopted in “The Geology of Tasmania.” 
The whole subject of causation is treated separately here- 
after. 
