The Geography of the Region about Devil's Lake and the Dalles of the Wisconsin

The Geography of the Region about Devil's Lake and the Dalles of the Wisconsin is a geographical work by Wallace Walter Atwood. Atwood was an American geographer and geologist. Excerpt:

"Elements of erosion.—The general process of subaerial erosion is divisible into the several sub-processes of weathering, transportation, and corrasion. Weathering is the term applied to all those processes which disintegrate and disrupt exposed surfaces of rock. It is accomplished chiefly by solution, changes in temperature, the wedge-work of ice and roots, the borings of animals, and such chemical changes as surface water and air effect. The products of weathering are transported by the direct action of gravity, by glaciers, by winds, and by running water. Of these the last is the most important. Corrasion is accomplished chiefly by the mechanical wear of streams, aided by the hard fragments such as sand, gravel and bowlders, which they carry. The solution effected by the waters of a stream may also be regarded as a part of corrasion. Under ordinary circumstances solution by streams is relatively unimportant, but where the rock is relatively soluble, and where conditions are not favorable for abrasion, solution may be more important than mechanical wear."