IN 1970 MARGARET Atwood, known only in small, mostly Canadian circles for her poetry, published a book entitled The Journals of Susanna Moodie, a persona poem sequence written from the point of view of a legendary 19th-century Canadian pioneer who had encountered the notorious murderess Grace Marks on a visit to a lunatic asylum. Grace had been alternately institutionalized and imprisoned for the brutal murders of her employer Thomas Kinnear and his lover/housekeeper Nancy Montgomery, spared from the sentence of hanging her accomplice James McDermott because of a shadow of doubt about whether she was temptress or victim. Out of this rich documented history, Atwood, 26 years