Canada's oldest trees may not be in the old-growth forests of British Columbia, but in fossilized form in New Brunswick, geologists say.

A forest of 345-million-year-old trees sticks out of a rock face outside Sussex, N.B., about 65 kilometres from Saint John.

The fossilized forest was exposed during construction of a new section of a highway.

Randall Miller, a geology curator with the New Brunswick Museum, found the stand while looking for roadside fish fossils six years ago.

"My first impression of them was with my nose a few inches from the outcrop walking along and seeing the base of a tree and thinking 'oh, isn't that odd, you don't normally see them this way,'" recalled Miller.

When Miller stepped back, he saw it was a whole forest standing on end, sideways. The trees extend on and off the road for 10 kilometres.

Researchers have identified more than 700 trees, which they describe in this week's issue of the Journal of the Geological Society, an academic publication in Britain.

The trees were like moss-like plants that grew to 20 metres high, according to the scientists.

"What's amazing about these particular New Brunswick forests is how dense they were," said paleontologist Howard Falcon-Lang of the University of Bristol. "It would almost be like squeezing through a bamboo thicket."

The newly discovered forest is fragile and is already eroding. Huge chunks of material have tumbled into the ditch.

Miller and Falcon-Lang aim to study the trees before they disappear, and they hope to have the site protected as a heritage site.