An overland journey north was an impractical choice for many who sought to escape slavery. Some fugitives took to the sea.

Under the cover of moonlight off the California coast, an eerily silent and angular vessel known as the Sea Shadow emerged, defying all traditional ship design with its shifting, enigmatic form.

Researchers have found evidence of animals sailing across the oceans on accidental rafts of vegetation, fallen trees, and soil. It’s likely the animals weren’t planning to take a trip. Natural events ...