Novelist Markson, while a graduate student at Columbia in 1951, wrote a maslet's thesis on Lowry's Under the Volcano, which had been published only four years earlier. A subsequent epistolary, then personal friendship with Lowry ensued, which Markson here remembers in a small essay, but the bulk of the book seems essentially to be that almost 30-year-old thesis, a ""Joycean reading"" of the novel that minutely crosshatches its references to Dante, the Faust legend, kabhalah, Edenic myth, the Grail quest, occultism, and loads more arcana. Markson introduces his chapter-by-chapter X-ray uneasily, saying ""this book gets better,"" as indeed it does toward the last chapters, but never enough to shake off the pall of too much score-keeping, too much echo-chambering. Congruences and deep structures and sources there are galore in Under the Volcano; Lowry's letter of 1946 to his English publisher, more or less explaining the book and pointing out its resonances, settles the chicken-or-the-egg question--but Markson never once looks up from his skein. Had he done so, he might, with his obvious devotion and knowledge of the work, have given not a gag of footnotes but a serious, independent critical consideration of one of the most hauntingly powerful and sublimely flawed novels of this century's second half.