OUR NATIONAL PARKS by John Muir (Sierra Club: $10). This series of descriptive essays was written for the Atlantic Monthly almost a century ago and published in book form in 1901. Typically, Muir celebrates the beauties of nature (especially his beloved Yosemite Valley) in enraptured catalogues of flowers, birds, animals and rock formations. But the upbeat tone suggests that he had been infected with the optimistic sense of progress that permeated the conservationist movement during the 1890s. He cheers the growing numbers of people visiting the newly established national parks ("Thousands of tired, nerve-shaken, overcivilized people are beginning to find out that going to the mountains is going home, that wilderness is a necessity and that mountain parks and reservations are useful not only as fountains of timber and irrigating rivers, but as fountains of life") unaware that the annual number of visitors would swell from a few thousand to millions and threaten the wildlife that the parks were created to preserve. Muir's impassioned prose offers interesting background reading for participants in the ongoing debate over the most desirable ways of using public land.