The type of rock underlying a lake is important in determining the chemical character of a lake. Lakes found entirely on Precambrian Shield 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.

 

A report on the geology of White Lake, authored by P.S. Peach, was first published in 1948 by the Ontario Department of Mines:Preliminary Report on the Geology of Darling Township and Part of Lavant Township, Lanark County. The final report, published as part 7 of the Ontario Department of Mines Annual Report Vol.65 (1956), and entitled the Geology of Darling Township and Part of the Lavant, can be downloaded here. The entire Volume 65 of the Annual Report of the Ontario Department of Mines can be downloaded by clicking on this sentence.

 

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 western shore of the lake is composed of granites, granite gneiss and syenite. These rocks we associate with Precambrian Shield. The map also shows that the lake itself and it's eastern 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. White Lake only abuts on shield type rocks and the chemical composition the lake water is not appreciably affected by this contact.

 

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.