Book excerpt: Clarence Glacken wrote one of the most important books on environmental issues published in the twentieth century. His magnum opus, Traces on the Rhodian Shore, first published in 1967, details the ways in which perceptions of the natural environment have profoundly influenced human enterprise over the centuries while, conversely, permitting humans to radically alter the Earth. Although Glacken did not publish a comparable book before his death in 1989, he did write a follow-up collection of essays—lost works now compiled at last in Genealogies of Environmentalism. This new volume comprises all of Glacken's unpublished writings to follow Traces and covers a broad temporal and geographic canvas, spanning the globe from the mid-eighteenth to the mid-twentieth centuries. Each essay offers a brief intellectual biography of an important environmental thinker and addresses questions such as how many people the Earth can hold, what resources can sustain such populations, and where land for growth is located. This collection—carefully edited and annotated, and organized chronologically—will prove both a classic text and a springboard for further discussions on the history of environmental thought.