This trip is less luminous than the title suggests, but worth taking. And what a wonderful title for a travel book. It is also full of paradox, since the author spends most of his time under the canopy of the world's most extensive rain forests. One is Amazonia, a great leitmotif in exploration fantasy and the most daunting landscape in the Western Hemisphere. The other is in Zaire, in the heart of Africa.

The writer, author of a previous book about the Amazon, approaches both regions with energy and knowledge and an absolute lack of pie-eyed romanticism. Indeed, if the first section of "In Southern Light" has a weakness, it is Shoumatoff's breezy familiarity with a subject often too exotic for residents of relatively arid, industrial societies.

"In the Realm of the Amazons" begins with a long, scholarly treatise on the environs of the river Nhamunda', which feeds into the Amazon from the north. Small by Amazonian standards -- only 375 miles long -- the Nhamunda' rises in mountains near the Guyana border and was reportedly dominated by independent, warlike women at the time of the Conquest.

These Amazons took men as lovers and then drove them off after the women had become pregnant, assuring the survival of the clan. A properly skeptical Shoumatoff goes in search of them, picking up along the way a collection of muiraquitas, amulets of carved stone and pottery that apparently litter the landscape the way Diet Coke cans do some of our parks. I won't reveal whether he finds Amazons, but the men he meets along the way don't seem a match for these mythic women.

The best travel writing -- the best of most writing, in fact -- is a combination of revelation, delight and some hardship. With Shoumatoff in Amazonia we get the first two but no sense of difficulty and certainly not of danger. The closest we come is the discovery that his guide has brought along insufficient gas to take them to the headwaters, the object of the trip, which is a disappointment to both author and reader. Shoumatoff makes the best of it, but the feeling of incompleteness lingers after he has so carefully set up the scholarly premise for the trip.

The African section is more successful, for two reasons. That continent is more accessible to the average American than the one directly south of us, with some cultural handholds for the struggling armchair adventurer; and here the author is actually trekking rather than sitting in boats and airplanes. He has gone to Africa to look up an old prep school chum and Harvard graduate whosought professional satisfaction in the study of rain forest fauna, first New World monkeys, then hunter-gatherers of the Zaire basin.

Shoumatoff is introduced to some Efe people, who take him off toward Moto Moto, not a sporting event but the last village in Ituri and one of the wildest parts of Africa. Here a certain schoolboyish enthusiasm takes over the narrative. He is a muzungu -- a Swahili word for white man vaguely equivalent to gringo -- and often the object of fear. Shoumatoff seeks to counteract it with gifts and medicine in the hallowed tradition of western ramblers in steamy terrain.

Meanwhile he observes at close range exotic plants and animals that the rest of us dream of. Somehow it is comforting to learn that Africa is still there, still savage in parts and at least partially immune to the homogenizing effects of western culture. The Africans themselves, including pot-smoking pygmies, emerge as affectionate sources of wisdom and delight. At one point his guide, Gamaembi, says of the glories of trekking in the bush, "I love the forest, monsieur. To know its situation, to find all the marvelous little things and the mountains in it."

That is a fair description of the joys of life anywhere. Shoumatoff's writing is full of those marvelous little discoveries, with a mountain or two thrown in.