146 NOTES ON THE GEOLOGY OF LAKE ST. CLAIR. 
Lake St. Clair, Lake Echo, Lake Arthur, Nineteen Lagoon, 
Lake Sorell, Lake Crescent, and Great Lake on Great Plateau, 
and Lake Youl on Ben Lomond. 
5. By the irregularities of surface caused by ice sheet 
movements, asin the northern parts of Europe and North 
America; leaving, on the retirement of the ice, clay and 
mound enclosed hollows, forming, subsequently, numerous 
tarns and lakes. 
6. By the irregular erosion of valley systems, leading from 
high table lands and mountain chains, by former glaciers, of 
which, Lakes Undine, Dixon, George, Rufus, Dora, Spicer, 
Beatrice, Augusta, Edgar, and innumerable other lakes and 
tarns in similar situations in Alpine Valleys in Tasmania 
afford good local examples. Dr. Wallace has attempted to 
show that glacier regions and lakes and tarns are constant 
concomitants, and by inference these are desired to be 
regarded as cause and effect. But in the light of the preceding 
review of the mutability of causation, there is surely a better 
reason to be given for the prevailing concomitance in the 
higher latitudes of Europe and North America, and the 
absence of numerous lakes in lower latitudes, except, as he 
allows, in volcanic regions. May tne absence of lakes in the 
lower levels of low latitudes be not better accounted for, 
partly by the absence of precipitation, as in desert regions, 
and partly by rapid evaporation exceeding precipitation in 
other lower levels of warm regions ? 
On the other hand, as igneous rocks are also largely 
characteristic of the higher altitudes of all great mountain 
chains, peaks, and plateaux of glacier and other regions, 
may not be irregularities of surface produced on the surface 
of such rocks in glacier regions, caused by an unequal 
cooling, anastomoses of flow and violent alterations of level 
by upheaval, account for a larger number of the lakes in 
glacier regions than even the admittedly numerous examples 
which may be fairly referred to glacier erosion alone ? 
These are considerations well worthy of close attention, 
and whatever differences of opinion may still exist, it is hoped 
that the experience gained by the study of the numerous 
lakes of Tasmania may be of some service in arriving ata 
true conception of the whole subject. 
