Limberlost is located on the Canadian Shield, which is the largest exposure of Precambrian aged rock in the world and covers nearly half of Canada.
Limberlost lies in an area of the Canadian Shield in which these rocks were once buried deeply under the Earth’s surface. In a collision of ancient continents they were thrust up to form hills and in some cases large mountain ranges.
During this mountain-building period the rocks were baked, squeezed, stretched and folded under immense temperatures and pressures.
Over millions of years, wind, rain and ice eroded these ancient mountain ranges to expose the hard metamorphosed granites, that were once deeply buried and today are the most prevalent type of rock found on the Limberlost property.
These metamorphic rocks probably came under intense heat and pressure a number of times, causing their texture and mineral content each time to change from their original form. A simple analogy would be the transformation of flour, yeast and water into bread when they are subjected to heat.
Following this process, subsequent geological shifts cracked the Earth’s crust, creating fault lines which led to grinding, crushing and pulverizing of the rock along the faces of these fault lines, resulting in small cracks as well as large gaps. In some cases these were filled with a mixture of molten feldspar, quartz or even more valuable minerals.
Although rocks in the Muskoka region date back over one billion years, Limberlost’s present physical features are mainly the result of more recent geological events which began less than two million years ago.
In what are known as the Great Ice Ages, vast sheets of ice began to descend beyond the polar regions to cover most of Canada.
Often two kilometres thick, these glaciers moved and picked up loose chunks of bedrock which ranged in size from small pebbles to house-sized boulders. These in turn scraped and scoured the bedrock, deepening any pre-existing zones of weakness such as fault and joints.
About 18,000 years ago, the last of the glaciers began to melt and about 8,000 years later the Muskoka region was again free of ice.
The repeated advances and retreats of continent-sized glaciers played a major role in shaping the surface of Limberlost as it is today. They removed pre-existing sediment and soils, carved, scoured and smoothed bedrock surfaces and deposited layers of sediment up to 200 metres thick in some places. As a result, Limberlost has ample sand and gravel deposits for road building as well as the longest continuous sandy beach in the Muskoka region. In addition, it has a mica and garnet deposit which was mined commercially in the 1940s, a very large quartz outcrop and numerous other unusual rock formations.
Although not as dramatic as a two kilometre thick glacier, other natural forces continue to make changes, ever so gradually, on the surface and form of exposed rocks on the Limberlost Reserve. Temperature variations, moving water, ice, gravity and even lichen and fern growth contribute to breaking down and disintegrating rocks on the reserve.
** Prepared with assistance from Vince Vertolli, Royal Ontario Museum