142 NOTES ON THE GEOLOGY OF LAKE ST. CLAIR. 
field for original investigation in the future, as at present we 
have only a very bald view of its history and stratigraphic 
sequence. It is here that the Tasmanian geologist in the 
future may expect to win fresh laurels, rather than in the 
immediate vicinity of Lake St. Clair, just lying beyond its 
most easterly limits, i.e., across the great eastern and western 
watershed-dividing ranges of Mounts Higel and Rufus. 
Southward across the Frenchman, Gordon River, Arthur 
Ranges, towards Port Davey, a still more interesting region 
awaits systematic exploration; for all that we know at present 
is, that the whole region is similarly occupied, mainly by the 
Lower Paleozoic and older Metamorphic rocks, whose geolo- 
gical history is still, practically, a closed book, and even its 
exact physiographical features are far from being perfectly 
delineated on our charts. 
ORIGIN OF THE Numerous Lakes, TARNS, AND LAKELETS. 
OF THE GREAT PLATEAU OF TASMANIA. 
While I am fully convinced that a large number of our 
small lakesand tarns,mostly carved outof the harder crystalline 
rocks, towards the mouths of the Alpine Valleys of our 
Western Highlands leading from the Great Plateau (such as 
Lakes Undine, Dixon, and Augusta), have been originated 
mainly by the agency of glaciers and their terminal moraines, 
I have, from long observation, arrived at the conclusion that 
our larger lakes on the higher levels of greenstone plateau— 
such as Lake St. Clair, Lake Sorell, Lake Echo, Lake Arthur, 
and Great Lake, together with innumerable lakelets and 
lagoons on the upper levels—have been mainly determined by 
the original irregularities of surface, produced partly by the 
anastomoses of successive flows of greenstones during their 
eruption, and partly by the unequal contraction due to lack 
of homogeneity of the cooling surfaces of the more massive 
horizontal flows of greenstone magma, which are so charac- 
teristic on the mountain plateaux of Tasmania, and which 
cover continuously, or in an anastomosing network of ranges, 
so large a portion of the superficial area of Eastern Tas- 
mania. This conclusion has again and again been forced 
upon my mind by the closer study of our upland lake 
systems, as it seems to account satisfactorily for all the 
known facts; and, moreover, it is in harmony with the views 
of leading physicists when contemplating the causes which 
produced the initial and universal irregularities of surface on 
our globe, and which in their turn determined the limits of 
land and sea during the later epoch in its history, which 
marked the stage of change from the expansive free gaseous 
envelope of vapour to precipitation and condensation from 
cooling and gravitation, in the form of lake, river, sea, and 
