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NOTES ON THE GEOLOGY OF LAKE ST. CLAIR 
AND ITS IMMEDIATE NEIGHBOURHOOD, 
TOGETHER WITH OBSERVATIONS REGARDING 
THE PROBABLE ORIGIN OF OUR NUMEROUS 
TASMANIAN LAKES AND TARNS. 
By R. M. Jounston, F.L.S. 
Apart from the unrivalled beauty of the scenery, there is 
nothing particular in the geological features of Lake St. 
Clair and its immediate neighbourhood, which is not common 
to and far more perfectly represented by nearly all the 
elevated greenstone mountains and plateaux, which form the 
most familiar physiographic features of the greater part of 
Tasmanian landscape. The great elevated greenstone plateau 
of Tasmania—which occupies so large a portion of our 
island, and not only embraces the Lake St. Clair region, but 
also includes the greater portion of our notable mountain 
peaks and bosses—is of the most uniform and simple 
character, of which the following divisions, where perfect 
sections are disclosed, may be regarded as more or less 
constant and typical, taken in ascending order :-— 
GENERAL CHARACTERISTICS. 
1. Base either (a) slates, schists, limestones, or conglome- 
rates of Upper or Lower Silurian age, as at Mount Tyndall, 
Eldon Peak, Eldon Bluff, La Perouse, Adamson’s Peak, Ben 
Lomond on one side, and Mount Picton, or (6) Archean or 
Metamorphic Rocks, as at Amphitheatre, Mount Gell, Mount 
Hiigel, Mount King William, Little Sugar Loaf, Gould’s 
Sugar Loaf, Mount Ossa, Mount Pelion, Barn Bluff, Cradle 
Mountain, Mount Manfred, and Du Cane Range. 
2. Permo-Carboniferous Rocks, with their varied divisions 
of grits, conglomerates, mudstones, blue slaty shales, im- 
pure limestones; winged Spirifer, Productus, Stenopora, and 
Fenestella Zones; Lower Coal Measures (Tas.), with 
Glossopteris, Gangamopteris, and Negarathiopsis; common 
throughout Hastern Tasmania. 
Middle Coal Measures (Tas.), with 
Gangamopteris and Vertebraria, as on Ben Lomond, 
Mount Cygnet, and slopes of Mount Wellington. 
| _ 3. Lower Mesozoic Sandstones, with Vertebraria and remains 
of ganoid fishes, as on slopes of Mount Wellington and Mount 
