Common menu bar links

Bruce Peninsula National Park of Canada

Geology

Cave Overlooking Georgian Bay
Cave Overlooking Georgian Bay
© Parks Canada/ PB Collection

The Niagara Escarpment runs from Niagara Falls to Tobermory. It forms the backbone of the Peninsula and shapes the northern boundary of most of the park, providing our new park with some of its most spectacular scenery. The rock of the Escarpment is very old.

Approximately 400 million years ago, this area was covered by a shallow tropical sea teeming with life in the form of plant-like animals, crustaceans, living corals and mollusks. It would have looked much like the present-day Great Barrier Reef of Australia. When the sea began to dry up, the minerals dissolved in it became more and more concentrated. Magnesium in the water was absorbed into the limestone, which then became a harder, slightly different sort of rock, called dolomite.

Overhanging Point
Overhanging Point
© Parks Canada/ PB Collection

The harder dolomite limestone forms much of the rock of the escarpment cliffs along Bruce Peninsula National Park's Georgian Bay shoreline. At Niagara Falls, the dolomite "caprock" erodes more slowly than the rock below it, creating the sculptured cliffs for which the area is famous.

Since the last Ice Age, water levels in the region have undergone great changes. Softer limestone has been eroded away by water action, leaving magnificent overhanging cliffs at various points along the shore. These are the big attraction of the Cyprus Lake trails.

Overhanging Point
Overhanging Point
© Parks Canada/ PB Collection
Where erosion has cut more deeply, caves have been formed, like the Grotto on the shore between Marr Lake and Georgian Bay Trails. Great blocks of dolomite, undercut by wave action, have tumbled from the cliffs above and can be clearlyseen below the surface of the deep, clean waters of Georgian Bay.

Limestone is a rock which is easily eroded by water, as is shown by the "sculpted" appearance of much of the rock in the park. You may see rock covered with small circular holes. This is called "pitting" and is caused by mild acid in the water dissolving the rock.