If canoeing down a slow river is your idea of fun, you may enjoy this travelogue from Leff, an author (The Last Undiscovered Place), poet and former deputy environmental commissioner of Connecticut. Retracing a short trip down the Concord and Merrimack rivers taken by the Thoreau brothers in 1839, Leff doesn't leave the babbling to the water, lecturing readers and occasional co-travelers (his son, his girlfriend, his neighbor). The idea he calls ""deep travel"" is an investigative-improvisational mode of travel that requires extraordinary attention: ""One observation leads to another and questions beget... delicious distractions."" Leff travels through former mill towns and defunct canals, paddling waters wide, narrow, polluted and occasionally populated. Leff weaves heavy-handed history lessons into the narrative, researched and presented as meticulously as Thoreau's work. Along with standard nature issues like disappearing bird species and industrial development on New England's waterways, ""delicious distractions"" include fatherhood, love and city planning. Leff's ""forensic"" sensibility (""to see the landscape as the coroner sees a body"") makes this an intersection of the clinical and the transcendental: a detailed, dense journey, reminiscent of Thoreau's own work.