The type of rock underlying a lake is important in determining the chemical character of a lake. Lakes found entirely on Precambrian
rocks are more sensitive to acid rain and have less of a capability to adjust to changes in acidity (pH). They may also be
very low in calcium making it difficult for fish and other organisms to thrive. Lakes found entirely on carbonacious rocks (limestone,
calcite) are better at maintaining a pH balance (buffering capacity), but are usually higher in calcium content making them more
likely to provide suitable habitat for invasive species such as the zebra mussel. White Lake falls into the latter category.
The geological map (reproduced below), which was part of the above cited report, clearly shows the nature of
the rocks underlying White Lake. White Lake can be seen on this map in the upper right hand corner. The map legend indicates that
the entire northern shore of the lake is underlain by granites, granite gneiss and syenite. These rocks we associate with Precambrian
Shield. The map also shows that the lake itself and it's southern shore is entirely underlain by sedimentary rocks such as crystalline
limestone, including dolomite. Indeed, the Tatlock calcite mine is only a few kilometers from White Lake.
A more recent description
of the geological setting for White Lake can be found in the 1988 Ontario Geological Survey Open File 5693: R. M. Easton, Geology
of the Darling Township Area, Lanark and Renfrew Counties, pp. 265. The download link can be found HERE
Because White Lake is
in contact with both granites and sedimentary rocks, the lake has developed a unique character. It has good buffering capabilities
guarding against changes in acidity while at the same time has a relatively high content of calcium measured at about 35 parts per
million. Click HERE
for additional information on the geology of White Lake and a coloured geological map. The full version of the
map showing greater detail and adjoining areas can be viewed and downloaded HERE.
Geological Setting of White Lake