Richard Snow has provided an intriguing, off-handed history of American railroading--its technological development, economic impact, odd characters, legends, and lore. David Plowden has contributed some handsome, often stirring photos of railway operation. But seldom do the twain meet, and almost never to specifically illustrate the text--which almost always cries out for illustration, for the kind of contemporary documentation found in the American Heritage volumes. Another problem is the fiat, picture-book format, which suits an audience considerably younger than that addressed by Snow's lightly sophisticated text. He's dandy on such relative esoterica as the confrontation between clergy (no Sunday operation) and commerce, the constructive role of hoboes, the transformation of ""The Big Rock Candy Mountain"" from a bitter, ironic ballad (sung by a cynical hobo) into a utopian hymn ""to the land where the hoboes' road ended."" And he'll tell you tho whole story of Casey Jones and the song that bears his name. But exactly who will settle down to the text--and more or less disregard the inappropriateness of the pictures--is hard to determine.