From a letter of Herman Melville’s – March 3, 1849, pages depend on which edition of correspondence you pull from but it’s also heavily quoted elsewhere.
Now, there is a something about every man elevated above mediocrity, which is for the most part instantly perceptible … I love all men who dive. Any fish can swim near the surface, but it takes a great whale to go down stairs file miles or more; and if he don’t attain the bottom, why, all the lead in Galena can’t fashion the plummit that will. I’m not talking of Mr. Emerson now, but of the whole corps of thought-divers that have been diving and coming up again with blood-shot eyes since the world began.
Extracts 