Discover Toronto's history as told through its plaques

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Dolostone

Photo by Alan L Brown - Posted June, 2007

Photo by Alan L Brown - Posted November, 2013

Attached to this rock here in front of the Toronto District School Board offices at 5050 Yonge Street is a plaque which says:

Coordinates: 43.767216 -79.412742

This block of dolostone, a magnesium-rich variety of limestone, was found buried in boulder-studded clay about 10 metres below the surface during the excavation of the Yonge Street subway in August of 1972. Outcroppings of dolostone are found generally in southern Quebec and probably this stone, weighing seven tonnes, was transported by glacial ice along the St. Lawrence Valley some 13,000 years ago.

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Precambrian Erratic
Igneous Boulder

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Geology

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