JAGUARS RIPPED MY FLESH Adventure Is a Risky Business By Tim Cahill Bantam. 306 pp. Paperback, $8.95

Irreverence is a specialty of Tim Cahill's generation, and he ranks among its apostles. One of the writers who helped Rolling Stone's Jann Wenner launch Outside magazine in 1976, Cahill generally steps into the outdoors with tongue in or near cheek, as the title of his new book suggests. (For the record, he has substituted Jaguars for Weasels in borrowing Frank Zappa's memorable album title, "Weasels Ripped My Flesh.")

Consider, for example, his participation in a trek to pre-Columbian ruins in northern Peru. With mock imperialism he decides to name the ancient fort he and his colleagues stumble upon. Never mind that the local Indians have known its whereabouts forever. He is the explorer, and his the prerogative to bestow the name Fort Big Tim Cahill. "This is a good name," he reflects, "and I think it sings." Elsewhere he links the urge to conduct Guinness Book forays into such perilous places as Antarctica "with the desire to see just how truly rotten life can be."

The funniest pieces in this collection from the pages of Outside, the late Geo and other magazines constitute what might be called the Tim Tries Sequence. Rock-climbing, hang-gliding, parachute-jumping, ballooning, cave-exploring, hurricane-eye-flying (as a passenger, not a pilot), Cahill Just Says Yes to them all. He portrays his editors as a passel of knee-slapping sadists whose chief pleasure in life consists of landing him in some new, terrorizing soup.

What lifts these pieces above the level of counterculture high jinks are the quality of Cahill's prose and the depth of his knowledge. He can evoke natural phenomena as vividly as any writer I'm familiar with. This, for example, is from his sketch of the devastated earth near post-eruption Mount St. Helens: "The color below is constant, a combination of the brown of the mud and of the black and the yellow-white of the ash. It is like no other color on the face of the earth, and it stretches, constant, from horizon to horizon. It insults the eyes, this color, and it will not allow the mind to fasten upon it. The color excites a sense of horror: it is like looking at the carcass of a skinned animal."

His informed explanations of natural processes include why trees split in the bitter cold of a Yellowstone winter (the sap inside them expands when frozen) and how turtles probably evolved ("from a marsh-dwelling lizard that hunched its shoulders forward, protecting its head with hard scales, in case of attack").

The turtle essay, "The Shame of Escobilla," is indeed the book's soul -- one of the most effective examples of environmental reporting ever published. Here we see a somber Cahill -- no jiving, no mugging -- on a visit to a Mexican beach where a local grandee has built a hatchery to save the Olive Ridley sea turtle. Or so it seems. As Cahill stays on the scene, missing his plane home, probing more deeply, certain anomalies crop up. The number of female turtles hitting the beach for egg-laying sessions has been plummeting in recent years. The hatchery tubs are in use only on the day a camera crew shows up to film the operation, and the hill of slaughtered turtles at the dump out back suggests a quite different purpose. Money unloosens some tongues, and Cahill realizes he is dealing with a slaughterhouse in disguise. Although the jury is still out on whether the Olive Ridley will recover from this butchery, the species undoubtedly has a better chance thanks to Cahill's article.

Its intrinsic worth aside, this book is valuable as a cultural document. Cahill's persona epitomizes every educated baby-boomer's dream. We could party as much as we wanted -- sampling drugs, rock 'n' rolling, engaging in daredevil sports, and generally postponing adulthood far longer than any previous generation did -- but when we finally put our minds to it, we could get serious and make the world a better place. With his "redemptive" sea-turtle expose', Cahill seems to have pulled off just such a feat. The reviewer is a Washington writer and critic