Adolphe Morlot, in 1854, discovered fossils of temperate plants between layers of glacial deposits, and advanced the theory that there had been warm periods as well as cold ones during the Great Ice Age. In his “Notice sur le Quaternaire en Suisse” he suggested three separate glaciations with two warm interglacial periods between. In 1874 James Geikie, the geologist of Edinburgh, brought out his _The Great Ice Age and Its Relation to the Antiquity of Man_, building upon Morlot’s work; and his _Prehistoric Europe_, in 1881, expanded the glaciations to six. Yet for thirty more years some stubborn scientists still believed in a single glaciation. It was not until the turn of the century that the work of Albrecht Penck and Eduard Brückner established the history of the Alpine glaciations on a solid scientific foundation that has endured pretty well till today. They found four major glaciations and named them in neat alphabetical order after four Alpine valleys—Günz, Mindel, Riss, and Würm.[3] They divided the Würm glaciation at first into two periods of activity, and later into a number of smaller oscillations toward the end. There has been some controversy over the subdivisions of the Würm, and one to three Danubian glaciers have been suggested hundreds of thousands of years before the Günz; but the general hypothesis brought forward by Agassiz and the amplifications of his successors are now definitely established. With all this goes much knowledge of the ice sheets that covered Scandinavia, northern England, and Germany as far south as Dresden, and North America from ocean to ocean and down to Long Island and the Ohio and Missouri rivers. The End of the Great Ice Age Authorities agree that the last melting of the ice sheets and glaciers in the Alpine region began somewhere between 20,000 and 15,500 years ago. After considerable shrinkage and oscillation, the ice increased again for about 5,000 years, and then began to shrink once more. There is some disagreement as to when the Great Ice Age ended; a recent and very minor Daun glaciation has been rather rashly dated as late as only 3,500 years ago. These calculations are only for the Alpine region, and we must remember, of course, that the great ice sheets of northern Europe and North America behaved somewhat differently. [Illustration: THE ICE FIELDS OF THE LAST GLACIATION _At the height of the last glaciation 5,000,000 square miles of North America were covered with ice, as against 2,500,000 in Eurasia. The volume of ice was three times as great. The shore lines are those of the present rather than glacial time. (Map after Flint, 1957; Antevs, 1928; and Flint and Dorsey, 1945; estimates from Daly, 1934.)_]