BY R. M, JOHNSTON, F.LS. 145 
summarised as follows:—Lakes may be formed in several 
ways :— 
1. By subterranean movements, as in mountain-making, 
and in volcanic explosions, and as in the subsidence of the 
central part of a mountain system, which might conceivably 
depress the heads of valleys below the level of the original 
outflowing channel of stream, and as in the cup-like basins 
of extinct craters. Types of the latter are exemplified in 
Australia, by the Blue, Middle, and Centre lakes of Mount 
Gambier, and possibly some of the lakes of the Great 
Plateau of Tasmania. 
2. By ponding back of streams by lava. Type, Lake Aidat 
in Auvergne, and probably Lake St. Clair in Tasmania. The 
latter, however, can only partly be the result of this cause, 
for its great depth of 592 feet, in a trough of older rocks 
lying below the igneous flows, the igneous ponding flow 
being so much above its deep bed, the present head, now even 
180 feet below the lake surface, has by depression of the 
head of the valley, mainly aided in the formation of its 
great depth of water bed. The flow of greenstone which 
closes the mouth of the Lake, and through which its affluent 
the Derwent cuts its shallow course, would not, by itself, 
account for its present great depth; nor would glacier erosion 
account for ail its peculiar characteristics. 
3. By subsidence of surface, caused by the dissolution of 
rock salt, limestone, etc., such examples of the former occur 
in the Peak caverns of Derbyshire, grottoes of Anteparos and 
Adelsberg, and the vast labyrinths of the Mammoth Cave, 
Kentucky, and Salt Pans, Tasmania. Examples of the latter 
form are found frequently as small lakes and ponds in Tas- 
mania, as at the Circular Marshes and Ilfracombe. 
4. By the original irregularities of surface, produced by 
the irregular anastomosing flows, and unequal cooling of 
massive unhomogeneous igneous rock, as on the Great 
Plateaux of Tasmania; combined, probably also, with violent 
and abrupt alterations of level during the cataclysmic 
upheavals, which raised the rocks bodily, as on Ben Lomond, 
Mount Wellington, Great Plateau, and many other mountain 
table-lands, to a height of about 2,500 feet above their 
former levels. Geikie (p. 925, Text Book) states that most of 
the great table-lands of the globe seem to be platforms of 
little disturbed strata, either sedimentary or volcanic, which, 
as in the case of most of the elevated greenstone plateaux of 
Tasmania, “have been upraised bodily to a considerable 
elevation.” 
This cause, therefore, accounts most satisfactorily for the 
greater number of our elevated Tasmanian lakes, such as 
