THE OLD PATAGONIAN EXPRESS: By Train Through the Americas <i> by Paul Theroux (Houghton-Mifflin: $9.95)</i>

At a time when airlines emphasize the speed with which they transport people, Paul Theroux argues that traveling should be an end in itself: “We have become used to life being a series of arrivals or departures, of triumphs and failures, with nothing noteworthy in between.” His descriptions of the Latin American railways--both the gleaming modern marvels and the dilapidated wrecks--are vivid and evocative. Curiously, he never seems to like the places he visits or the people he meets in his travels: He maintains a disdainful superiority, like a minister’s wife accepting a contribution from the local madame. The results are interesting, but cold; from Boston to Patagonia, Theroux observes life without partaking of it.