Moby Dick: Sulphur Bottom Whale

Re the Sulphur-Bottom (Blue) Whale in Melville's time:

BOOK I. (FOLIO), CHAPTER VI. (SULPHUR-BOTTOM). — Another retiring gentleman, with a brimstone belly, doubtless got by scraping along the Tartarian tiles in some of his profounder divings. He is seldom seen; at least I have never seen him except in the remoter southern seas, and then always at too great a distance to study his countenance. He is never chased; he would run away with rope-walks of line. Prodigies are told of him. Adieu, Sulphur Bottom! I can say nothing more that is true of ye, nor can the oldest Nantucketer.