When a rock, loosened from its ties in the hills, once becomes a wanderer, it is restless ever after, and stirs in its sleep. Heat and cold expand and contract it, and make it creep down an incline. Hitch your rock to a sunbeam, and come back in a hundred years, and see how much it has moved.

The Writings of John Burroughs (Volume 19), Chapter II (p. 42)