In 1804, a pair of American explorers, Meriwether Lewis and William Clark, led an expedition from Illinois to points unknown, hoping to find a passage to the Pacific Ocean. Their round-trip took more than two years but was a success, with a well-developed series of maps showing how future pioneers could, similarly, travel westward.
Today, you can visit many of the sites where the Lewis and Clark Expedition set up camp if you’re so interested. And when you do, you can rest assured that those locations are historically accurate — we know many of the exact spots where the expedition set up camp. At first blush, you’d think that the detailed maps the expedition produced would be the source of those locations, but if you think about it for a moment, that can’t be true. Mapmaking of the time lacked the tools we have today — aerial cameras, satellites and GPS technology, surveying tools, and more. In fact: Lewis and Clark didn’t even have a pre-existing outline of what the continent looked like.
So, how do we know where Lewis and Clark went?
Because we know where Lewis and Clark went.
Okay, maybe the italics there are a little too subtle — let’s spell it out. In at least one case, we know where Lewis and Clark’s team set up latrines.
Just like cartography has advanced in the superseding 200 or so years, so has medicine. When the expedition set out on their adventure in 1804, they knew they’d need medical supplies and, specifically, something to fight off illness. A common treatment at the time was something called calomel, a laxative which, on the plus side, killed bacteria. On the minus side, though, was the reason why: calomel is a mineral which contains a high amount of mercury, and it was as toxic to humans as it was to the bacteria. That’s why we don’t use it today, at least not for medicinal purposes.
But again, this was the early 1800s and no one knew that. (And even if they did, a decent chance at madness was perhaps a fair risk given the dangers of an untreated bacterial infection.) So when someone in their group fell ill, the plan was clear: set up camp, dig a latrine, have the sick take some calomel and do their business, hopefully, cover up the hole, and move on further westward.
Hopefully, the infirm felt better afterward. But either way, their leave-behinds have proven incredibly valuable for historians. Given a century or two, an unattended latrine will, by and large, begin to look like any other latrine — it’s just a hole, after all. But when the feces contain mercury — in amounts and clusters which shouldn’t appear in nature otherwise — a small, kind of gross clue stays behind effectively forever. If archeologists can find a latrine in the area where Lewis and Clark may have been, they can test it for mercury — and that’s exactly what they’ve been doing, reports io9.
So far, researchers have identified one site — Travelers’ Rest State Park in Montana — as definitely a Lewis and Clark (rest) stop based on the mercury in the latrines. But more, hopefully, will be identified over the coming years.
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