Symbolism, Imagery, Allegory
In "The Encantadas", Melville points out that there are two sides to a Galapagos tortoise. The top is "dark and melancholy", but when you turn it over its breast-plate has a "faint yellowish or golden tinge." (5.22) Bleak as the Galapagos are, they have their good side too—one of which is the turtles themselves, which Melville clearly enjoys describing, in all their ominous, slow-moving awkwardness.