HORSE HEAVEN HILL (216 pp.)Zone GreyHarper ($3.50).
Shortly before his death in 1939, Zane Grey wrote to Harper & Bros., his publishers, to say that he had three manuscripts ready for publication. Harper is still publishing themat the rate of one a year. By the time half a dozen posthumous novels of the early West had appeared, intramural smiles flickered through the book business. How long could Harper keep Grey alive? The explanation, say Harper editors, is really quite simple. Their man was so prolificwriting longhand on a lap board at the rate of 100,000 words a monththat no publisher could have...