Mark Twain observed and recorded many geological features during his travels around the world. He saw limestone pillars in Mono Lake, California, that rose twenty or thirty feet out of the lake. In Hawaii, he watched a volcano erupting on the floor of a crater that measured ten miles in circumference. He saw beds of pure oyster shells in Anatolia, interbedded with discrete layers of clay, that had been tilted and lifted five hundred feet above the...