Robert W. Chambers & Robert W. Chambers 
In Search of the Unknown [EPUB ebook] 

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.