A black cat crossing one's path to bring good luck is indeed an old English superstition; but we have the same ambivalence here, as black cats, along with frogs, were the animals most commonly held to be witches' "familiars" [ie creatures who attended them in the casting of their spells], and hence to be unlucky. It may be relevant here to draw attention to Edgar Allen Poe's famous story [which so terrified me in childhood!] 'The Black Cat'.