"Erratics" take their name from the Latin word errare (to wander). They often travel far distances and appear out of place compared to the geology in the local area. This particular boulder likely came from 2.3 billion year old outcrops of marble in the Grenville Province of the Canadian Shield, some 50 km northwards near Madoc, Ontario.

The sides were probably once marked by long linear scratches called 'striations' made by debris passing around the boulder. However, exposure to the elements and growth of lichens and mosses on the surface have largely destroyed any fine detail.

The boulder was transported from the Canadian Shield to it's current location under the power of the last great ice sheet to cover North America some 13,000 years ago. During this trip, it was embedded in sediment underneath the ice sheet, which scraped and shaped the boulder into it's current rounded form.

Marble is essentially metamorphosed limestone. During the Grenville Orogeny, the buiding of Appalachian-scale mountain ranges squeezed and heated layers of sedimentary limestone between colliding land masses. Calcite in the limestone was recrystallized into marble. Here we see a number of blocks of limestone with sedimentary layering intact.

The boulder was once buried in under 10-20 meters of till, but it has since been excavated, probably by glacial meltwater flowing along the Trent Channel.

This small creek is all that remains of a much larger proto-Trent river that carried meltwater away from the receding glaciers during deglaciation. It is now a marsh.

The Bleasdell Boulder is named after Reverend William Bleasdell who in 1862 first described the boulder in the scientific literature. The boulder is also sometimes called the Glen Miller Rock after the nearby town.

Welcome to the largest known glacial erratic in Ontario! The massive Bleasdell Boulder stands at 7.6 meters high and weighs a staggering 33,000 tons.

During the Grenville Orogeny, hot geothermal fluids migrating through these rocks reacted with the calcium carbonate in the marble to create a variety of alteration minerals including course quartz, actinolite, and tremolite. This type of altered marble is called "skarn".