Tarn was once primarily used in northern England as a name for a small, deep, self-contained mountain lake, especially those of the Lake District. In fact, the tourist boats of Lake Windermere today are known as Tarn Taxis. Since the 1950s, geologists have used the term to refer to lakes that occupy erosional basins or cirques, and it is now a synonym for cirque lake. What ponds were to Thoreau, tarns were to Wordsworth, who described one as “round clear bright as heaven” and another as “solitary.” But other poets, such as Edgar Allan Poe and A. E. (George William Russell), have found in the isolated depths of these glacial scours “dank” or “dark” qualities. Seamus Heaney, in his poem “Bogland,” about a very different landscape, refreshed the word in the following lines: “Everywhere the eye concedes to/Encroaching horizon, // Is wooed into the cyclops’ eye/Of a tarn.” Glacial tarns such as Duck Lake, Lake Virginia, Big Bear Lake, and Desolation Lake, to name a very few, dot the John Muir Wilderness in California’s Sierra Nevada.