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THE GEOLOGY OF THE LAKE ST. CLAIR DISTRICT, 
TASMANIA. 
GraHAM Orricer, B.Sc. 
(Maps.) 
In the following paper an attempt is made to give some 
account of the main geological features of the district about 
Lake St. Clair. The observations were made during a recent 
visit to the lake by a party, including Professor Spencer, of 
Melbourne University, myself, and several others. Owing to 
the inclement weather we experienced, we were unable to 
make as extensive observations as we would have wished, and 
the present account does not purport to be more than a 
geological sketch. 
Lake St. Clair is situated on the great central greenstone 
plateau of Tasmania. This plateau, according to Mr. R. M. 
Johnston, “preserves a general rugged or undulating level of 
about 4,000 feet altitude, and its higher bosses and peaks 
and its valleys do not vary much more than 1,000 feet above 
or below this uniform level.” Lake St. Clair, the queen of 
Tasmanian lakes, lies near the western boundary of this 
plateau, and a little to the north of the central part, its 
northern shore being cut by the parallel 42° S. lat. Its 
elevation above the sea is about 2,400 feet. It lies in a long, 
deep, narrow valley, bounded on the east by the Traveller 
Range and its offshoots, Mount Ida, and the rugged moun- 
tains between it,andthe Ducane Range, and on the west by 
Mounts Olympus, Byron, and Manfred. The length of the lake 
is about 11 miles, while its greatest breadth is about 2 miles. 
A depth of 590 feet is recorded. 
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 
sreenstone ridges and button-grass flats. The shores of the 
lake are remarkably regular, and at this end (southern) 
occur the only indents of importance, viz., Cynthia Bay on 
the W. and the lake basin-on the HE. The latter is almost 
land-locked. From it the Derwent starts on its way to the 
south. The lake is fed by numerous streams and torrents, the 
principal ones being the Narcissus (Hamilton) on the N., flow- 
ing from the Ducane Mountains; on the E. 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 560 teet, 
according to our aneroid, above it. The Cuvier flows down a 
