Because it all seems so improbable-so horribly impossible to me now, sitting here safe and sane in my own library-I hesitate to record an episode which already appears to me less horrible than grotesque. Yet, unless this story is written now, I know I shall never have the courage to tell the truth about the matter-not from fear of ridicule, but because I myself shall soon cease to credit what I now know to be true. Yet scarcely a month has elapsed since I heard the stealthy purring of what I believed to be the shoaling undertow-scarcely a month ago, with my own eyes, I saw that which, even now, I am beginning to believe never existed.