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Half-a-billion-years ago, the area of the future City of Westmount lay under an ocean. In fact, at the time, most of the world was under water, and the overall landscape of North America resembled a shallow, warm, tropical sea. There were no land animals as there was no land, except for a few small islands near the present Caribbean. Tectonic plates collided with each other, forming underwater mountain ranges, volcanoes and rifts, the predecessors of our present continents. (Modern humans first appeared on earth around 200,000 years ago – a wink in time as far as the history of the earth is concerned).  

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Ancient worm trails in 500-million-year-old stone at Selwyn House School facade.

During this period, known as the Ordovician Period (which lasted almost 70 million years, beginning 510 million years ago and ending 439 million years ago) this nutrient-rich water would give rise to the minute soft-bodied animals that would become the well-known Montreal limestone, (also referred to as Trenton limestone or greystone) that was used to build many of our homes and institutions.  As the aquatic animals died, they fell to the ocean floor, eventually building up a quarter-kilometer-deep layer of greystone sedimentary limestone. This layer of greystone was used as a building material for many of Westmount’s buildings.

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Complete brachiopods from Westmount and Montreal. They have turned to stone after millions of years buried beneath the earth.

“One inch of greystone represents about 10,000 years of sedimentation,” explained Ingrid Birker, a paleontologist and Science Outreach Coordinator with McGill University’s Redpath Museum. “It was a time when all these animals were invertebrates, with an exoskeleton or shell coverings or neither, (such as worms and other soft bodied animals like sponge). There were no animals with bones; real boney fish did not start appearing until 200-million-years later,” she stated.    

But you don’t have to go far to see the fossils these great seas left behind; in fact, you might not have to go much further than you doorway. Most of the greystone homes surveyed for fossils for this article contained shells and coral-like animals. Westmount City Hall has a fine selection of fossils on its exterior facade, you just have to get used to what you are looking for; but once you catch on, you start seeing them everywhere.

Other good locations for viewing fossils includes Selwyn House, the fire station on Stanton (near where an early greystone quarry was once located), and the former post office on Sherbrooke Street. Wherever you find greystone as a building material, Ordovician Period fossils are definitely nearby.


Brachiopods appear frozen in the greystone of a Westmount wall.

By the end of the late 19th century, greystone started falling out of favour as a building material, to be replaced by red brick. The great greystone era of Montreal was coming to an end.

Nowadays, greystone limestone is crushed as an aggregate in cement production or as filler for driveways and roadways; however, some greystone is still used as a principal building material and while its heyday is over, its beauty is very much in evidence, as a covering for our homes and institutions. 

For more information on fossils and fossil tours in downtown Montreal, contact Ingrid Birker of the Redpath Museum at ingrid.birker@mcgill.ca,  www.mcgill.ca/redpath/ , or call 514-398-4094. The museum is free and open Monday to Friday, from 9h-17h and every Sunday from 11h-17h. It is closed Saturdays.

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