WORK or GLACIERS. The moraines are carried along by the glaciers and deposited on the sides of its valley and at the end of the ice. Some rocks become imbedded in the ice and act like graving-tools in making long, straight scratches in the bed-rock, whose surface is also smoothed by finer material moved by the ice. A region which has been covered by a glacier usually shows smooth and rounded rock surfaces marked with parallel scratches; heaps of rocks, more or less angular, and dumped irregularly about, fre quently forming small lakes. These rocks are often of a different kind from the underlying country rock, showing that they have been trans ported from a distance, and their angular or subangular forms show that they have not been transported by water. They are called erratics. Among them some will have smoothed and scratched surfaces. It is by studying the dis tribution of scratches, smoothed surfaces, and er ratics, that geologists have been able to show the existence of a former ice age when large parts of Europe and of North America were covered by great sheets of ice.
The power of glaciers to erode valleys or lake basins has been greatly discussed, without a con clusion commanding general assent being reached.
Leading geologists entertain diametrically oppo site opinions on this subject.
BIBLIOGRAPHY. For general description and Bibliography. For general description and theoretical discussion of glaciers, consult: Shaler and Davis, Glaciers (Boston, 1881) ; Agassiz, Etudes sur les glaciers (Neuchatel, 1840) ; Schmidt, "Eine neue Glacialtheorie," in Peter mann's Mittheilungen, vol. xliv. (Gotha, 1898) ; Agassiz, Nouvelles etudes et experiences sur les glaciers aetuels (Paris, 1847) ; Agassiz, Unter suckungen fiber die Gletscher (Solothurn, 1841) ; Heim, Handbuch der Gletscherkunde (Stuttgart, 1885) ; Rendu, Theory of the Glaciers of the Savoy, translated by Wills (London, 1874) ; Forbes, Occasional Papers on the Theory of Gla ciers (London, 1859) ; Agassiz, Geological Sketches (Boston, 1890). Descriptions of indi vidual localities may be found in Reid, Studies of the Muir Glacier, Alaska (Washington, 1892) ; id., "Glacier Bay and Its Glaciers," in United States Geological Survey Report (Washington, 1895) ; Russell, Glaciers of North America (Bos ton, 1897); Tyndall, The Glaciers of the Alps (London, 1800).