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Historical Steamship Routes Traced by the Trail of Rocks They Left Behind

Source: Hakai Magazine/K. N. Smith - October 12, 2017 in Adventure

Historical Steamship Routes Traced by the Trail of Rocks They Left Behind
Photo: Princess Sophia/WIkimedia Commons (CC0)

A survey of marine life off the east coast of Australia pulled up several handfuls of history this summer, along with a distressing amount of modern litter. The historical artifacts don’t look like much—just some lumpy, ash-colored chunks of baseball-sized rock—but they trace the trails of steamships that plied these waters a century ago.

In the United States, the Great Plains still bear the scars of the Oregon Trail: deep ruts dug into the earth by the passing of thousands of wagon wheels. The ocean usually doesn’t keep such mementos; a ship’s track through the water is ephemeral. From the early 1800s to the mid-1900s, however, steamships inadvertently marked their routes with trails of clinker, a dense residue left after coal is burned.

Clinker is mostly slate and shale, fused into an ashy mass in the heat of the fire. As a ship steamed along, the crew periodically scraped clinker out of the firebox and tossed it over the side. Because the rock is so heavy, it sank quickly, hitting bottom right below where it was dropped. That, according to biologist Eva Ramirez-Llodra from the Norwegian Institute for Water Research, makes clinker uniquely good at marking the passage of ships on the surface. And because many steamships followed the same major routes around the world, ridges of clinker accumulated, leaving tangible trails.

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