PROCEEDINGS, JULY. XV 
It was an attempt to give some account of the main geological features 
of the district, from observations made during a recent visit to the lake 
by a party, including Professor Spencer, of Melbourne University, the 
writer, and several others. The inclement weather prevented extensive 
bservations ; therefore the present account purported to be nothing 
more than a geological sketch. Lake St. Clair is situated on the great 
central greenstone plateau of Tasmania, near the western boundary of 
the plateau, and a little to the north of the central part, ics northern 
shore being cut by the parallel 42deg. S. lat. The elevation of the 
Queen of Tasmania lakes is about 2,400ft. above sea level, and it lies in 
a long, deep, narrow valley, bounded on the east by the Traveller 
Range, and its off-shoots Mount Ida and the Rugged Mountains 
between it and the Ducane Range; and on the west by Mounts 
Olympus, Byron, and Manfred. The lake is 11 miles long, and its 
greatest breadth about two miles, with a recorded depth of water of 
590{t. At the north end the valley extends to the foot of the Ducane 
Ranges, some 10 miles beyond this extremity of the lake. The southern 
shore shelves up to a succession of low greenstone ledges and button- 
grass flats. The shores of the lake are remarkably regular, and at the 
southern end occur the only indents of importance —Cynthia Bay on 
the west and the Lake Basin on the east. The latter is almost land- 
locked. From it the Derwent starts on its way to the south. The lake 
is fed by aumerous streams and torrents, the principal ones being the 
Narcissus (Hamilton), on the aorth, flowing from the Ducane Moun- 
tains ; on the east a stream from Lake Laura, and another from the 
mountains behind Mount Ida; while Cynthia Bay receives the Cuvier. 
The latter river rises from Lake Petrarch, a small sheet of water just 
under Olympus on the opposite side from Lake St. Clair, and about 
560ft. above it. The Cuvier flows down a broad, undulating valley, 
known as the Vale of Cuvier. This valley runsin a S.E. and N.W. 
direction, and is bounded on one side by the Olympus Range, and on 
the other by Mount Hagley. The most important point at present in 
the geology of this district is the relation of the greenstone to the car- 
boniferous rocks. It may be said that Mount Olympus affords the 
key to the geology of the district. There seems to be no reasen to doubt 
that the sedimentary beds extend right along tothe N.W. extremity of 
the mountain, occupying the same position relative to the greenstone at 
this side that they do on the other. This is indicated by the numerous 
and often very large blocks of sandstone and conglomerate that occur 
mingled with masses of greenstone towards the upper end of the Cuvier 
Valley. The summit of Mount Olympus is much-like that of Mount 
Wellington. A noticeable feature was the presence of several large 
fissures, but as to their origin he did not care to speak definitely. 
Perhaps they were due to dislocations, perhaps to the undermining 
action of water in wearing away the underlying rock. The appearances 
seemed to him to point clearly to the greenstone beiny of later date than 
in the sandstone. No sign was seen of the older palzozoic rocks repre- 
sented in Mr. Johnston’s map as occurring in the Cuvier Valley. The 
origin of the lakes of the great central plateau, continued the writer in 
summing up, is a question which affords ample scope to any geologist 
who will undertake their investigation. Lake St. Clair was first sup- 
posed to be a crater lake, but of this there is no evidence. As Tasmania 
is undergoing a movement of upheaval the rivers must, geologically 
speaking, be rapidly lowering their channels. The course of the Derwent 
affords ample evidence of this. And thus the level of the Lake St. Clair 
waters must be gradually being reduced. From the top of Mount 
Olympus we counted about 30 lakes and tarns on the opposite plateau, 
occupying undoubted rock basins in the greenstone. We did not find 
the slightest trace of glaciation. I am much inclined to the opinion 
that most of the basins of the Traveller Plateau lakes will be found to 
