Limits of the Known, by David Roberts. 336 pp. New York: Norton ISBN 978-0393609868 Reviewed by Jonathan Dore After half a lifetime of mountaineering, and another half of canyoneering and writing books and magazine features, David Roberts has pulled together the various threads of his life in a book that is part memoir, part historical anthology of notable exploration, and part meditation on the meaning and limits of adventure and adventuring. Its summatory and valedictory flavour come from the autobiographical element, disclosed early on, that the author is living with an aggressive cancer (he guards us against the well-meant but double-edged metaphor of “battling” or “fighting” the disease), already spread and metastasized but against which, as of late 2017 when he finished writing, he was holding his own. Each of the seven chapters of this artfully constructed book interleaves an account of one or more historical expeditions with an episode or aspect of the author’s own life that r...