Brown's simple, load-bearing sentences can march on for pages with hardly a skip, let alone a pirouette. A quick glance will reveal dozens of nearly consecutive paragraphs beginning, ''She had rested . . .'' ''She was very thirsty . . .'' ''She didn't know . . .'' ''She could feel . . .'' and ''She waited. . . .'' Such Amish-plain descriptions of activity make up most of this novel's nearly 500-page bulk: ''He had to wait for two cars and then he mashed down on the gas and they headed out. He opened a beer and pushed a tape into the deck. She looked over at the gas gauge. It was full.'' When you get to that last sentence, with its slight, subjective salience, it's like coming across a grain elevator in Nebraska.