It wasn't far beneath the pavement on York Street that construction crews came across something unusual.

As they were digging up the roadway to replace the old sewer system in early May, they uncovered a few pieces of wood and concrete about a metre deep.

It didn't look like much. But the debris is actually a piece of London's long-abandoned streetcar system.

"It's basically railway ties that should have been removed decades and decades ago," said Larry Davidson, a senior technologist with the City of London's engineering department.

The streetcar system was created more than 140 years ago and used as a main mode of transportation through the city's core.

The London Street Railway Co. introduced the horse-drawn trolleys in 1875. Two decades later, the system was converted to electric streetcars.

Last remaining piece

The primary route ran along Dundas between Lyle Street and Clarence Street.

But by 1895, routes were connecting the downtown to Hamilton Road, Wharncliffe Road, Ridout Street and Richmond Street.

The system was eventually shut down in 1940. So finding pieces of that underground network is rare, according to Davidson.

London's streetcar system was initially horse-drawn until it was reverted to electric trolleys in 1895. (CBC)

He expects the latest discovery could be the final remaining remnant of London's streetcar system.

"I think it's the last of it just because it's been so long since it was abandoned," Davidson said.

"Most of these streets have already been worked on — new sewers, new infrastructure under it. If there was anything left behind then, it would have been found in that construction."

London says so long to the streetcar

The reason why London's streetcar system was disassembled comes down to cost, according to Dan Brock, a historian whose book 'Fragments of the Forks' explores London's past.

"It was more economical to use [buses] that were fuelled originally by gasoline and then diesel...you certainly didn't have to worry about laying down track and having electric lines." Brock said.

Larry Davidson, who oversees several construction sites in London, said the latest discovery is likely the last of the city's old streetcar system. (Julianne Hazlewood/CBC)

Ridership was another issue. Brock said the number of Londoners hopping on the city's trolleys started to dwindle as cars became more commonplace.

The London Street Railway Co. struggled to stay afloat during The Depression and a decade after shutting down its streetcar service in 1940, it was purchased by the city.

It became the London Transit Commission in 1951.

Pieces thrown out

The railway ties recovered by city crews have already been tossed out.

Larry Davidson from the city said the rotten wood is no longer worth recovering. But the city has recycled the pieces of concrete from the old streetcar system.

Construction crews on York Street are set to replace the old sewers and put in proper storm drainage. (Julianne Hazlewood/CBC)

And so crews will go on replacing the old sewer grates from the same era — late 1800s.

Davidson said he never knows what piece of London's history they may stumble upon next.

"It's always a mystery," said Davidson.