Unimaged

What form of speech may express the happiness of the one half-hour passed beside that lonely pool, which never before imaged a love-meeting so perfect in its affection?—the delicious silence broken by unconscious exclamations; the asking looks that question without a sound; the forgetfulness of past and future, as if life were centred in this one present and dearest dream. Let it pass unimaged, unless by memory.

What does the unimaged side of Mercury look like and what processes have influenced its surface?