The first two decades of the twentieth century will rank as a most distinguished era in the history of exploration, for during them many of the great geographical riddles of the world have been solved. This book contains a record of some of the main achievements. What Nansen said of Polar exploration is true of all exploration; its story is a "mighty manifestation of the power of the Unknown over the mind of man." The Unknown, happily, will be always with us, for there are infinite secrets in a blade of grass, and an eddy of wind, and a grain of dust, and human knowledge will never attain that finality when the sense of wonder shall cease. But to the ordinary man there is an appeal in large, bold, and obvious conundrums, which is lacking in the minutiæ of research. Thousands of square miles of the globe still await surveying and mapping, but most of the exploration of the future will be the elucidation of details. The main lines of the earth's architecture have been determined, and the task is now one of amplifying our knowledge of the groyning and buttresses and stone-work. There are no more unvisited forbidden cities, or unapproached high mountains, or unrecorded great rivers.