166 GLACIAL ACTION IN TASMANIA, 
being deposited in South Canterbury, New Zealand, in lakes 
fed with turbid water issuing from beneath glaciers. While 
the clays have been laid down in still water, it is equally clear 
that the coarse gravel and boulders in the bottom of the 
lead have been deposited in the bed of a running stream, 
and it is therefore evident that the valley of a once 
turbulent watercourse has been somehow converted into a deep 
and still lake. The stream appears to have run to the north- 
ward, in quite a different direction to the present Ring River, 
and the valley of the latter must have been eroded since the 
older river system was covered up and obliterated, for it cuts 
through the above clayey layers to some depth. Seeing that 
there are grounds for considering the valley of the Mackintosh 
to have been scoured out by glacial action, it seems reasonable 
to suppose that the old Ring River became dammed by the 
advancing ice and its valley converted into a lake, which 
became rapidly filled with glacial sediments. The ice-sheets 
still advancing probably performed much of the work of 
erosion of the present Ring River Valley. Lower down this, 
it may be mentioned, we have further proof in the finding of 
gravel terraces 200 feet above the present stream, that an 
older river system has been almost entirely obliterated. The 
clays of the Deep Lead, so far as yet known, are very free from 
fossils which would give evidence as to its age, but as work 
proceeds it is probable that some leaves will be found which 
will help us to fix their date. 
It has always been regarded by mining men as an un- 
common feature in connection with the Mount Bischoff tin 
deposits that there was little or no trace of tin ore in the rivers 
and creeks heading from the rich gravels on the Mount, it 
being usual under such circumstances for the ore to be 
found for miles down the streams draining from the 
lodes or older gravel deposits. As the plateau round 
Waratah is high enough to have been well above the 
probable snow-line at the time of the glaciation of the 
country further inland, it seems possible that the deep gorges 
of the North Valley and Arthur Rivers may have been glacier 
beds, a supposition which their depth and shape give some 
colour to. If these valleys were cut out by ice the stan- 
niferous gravels would have no opportunity of being sluiced 
over and over again in the streams, so as to distribute the 
ore alorg their courses for long distances, but would be swept 
clean away with other rock debris. Should evidence be by 
and bye obtained to bear out this explanation, it would have 
further interest as giving a clue to the time of glaciation, for 
the Waratah plateau consists of basalt of tertiary age, over- 
lying tertiary leaf beds, and the Waratah valley up to the 
railway station has been cat through these basalts. The 
basaltic outbursts appear throughout this colony to have been 
