The Lens of Time is a unique collaboration between two observers who have, for more than twenty-five years, been examining landscape change in the Canadian Rockies--national park biologist Cliff White and Canadian Rockies historian Ted Hart. Working with historical photographs, White has retraced the steps of the original photographers and taken new shots in the same locales, a technique known as "repeat photography." Comparing these images side by side, the authors show the dramatic changes to the Rockies landscape that have occurred over the years. The sets of photographs generally follow ecological regions moving west from Calgary and the foothills, ascending through the low elevation montane zone of Banff National Park, and upward into the lower and upper subalpine. The authors then follow the historic photographers' routes for brief forays onto the west slopes of the Rockies in the Columbia River watershed of British Columbia, and east into the Front Ranges along the Red Deer and North Saskatchewan rivers. Moving north, the photographs depict the high windswept alpine zone and glacial ice of the Columbia Icefield, before passing through Jasper National Park and turning eastward to descend to the parkland region at Edmonton, Alberta. Useful captions describe the landscape changes visible in each "then and now" view, and five essays more fully explore the historical, political, and ecological processes at work. Illustrated throughout with striking images, The Lens of Time is at once a showcase for the beauty of the Rocky Mountain landscape and a valuable source of information about ecological change in this world-famous region.