be left to determine. All that we need note is, that if there be any force in Professor Darwin's argument, it is obvious that the crust is possessed of great rigidity, and could not be readily deformed by the mere weight of an ice-sheet. According to Dr. Drygalski, however, the presence of an ice-sheet, by reducing the temperature of the underlying crust, would bring about contraction, and in this way cause the surface to sink. When the ice-sheet had disappeared, then free radiation of earth-heat would be resumed, the depressed isogeotherms would rise, and a general warming of the upper portion of the lithosphere would take place. But the space occupied by the depressed section, owing to the spheroidal form of the earth, would be smaller than that which it occupied before sinking had commenced, and consequently when the ice vanished expansion of the crust would follow, and the land-surface would then rise again. The whole question is one for physicists to decide upon, but I may point out that if Drygalski's explanation be well founded, then it is obvious that it throws no light upon the origin and subsequent disappearance of an ice-sheet. Somehow or other this ice-sheet comes into existence, and the cooling and contracting crust sinks below it; and that depressed condition of the glaciated area must continue so long as the ice-sheet remains unmelted. Re-elevation can only take place when, owing to some other cause or causes, the climate changes and the ice-sheet vanishes. Those who advocate the "earth-movement hypothesis" as an explanation of the origin of extensive glaciation have welcomed Mr. Jamieson's view as harmonising well with their conclusions. They contend, as we have seen, that glacial conditions were induced by an extensive upheaval of the crust in northern latitudes, accompanied by a depression of the Isthmus of Panama. They then proceed to point out that the ice-sheets brought about their own dissolution by pressing down the crust, and introducing with submergence a disappearance of glacial conditions. See now how much they take for granted. In the first place, they assume an amount of pre-glacial or early glacial elevation of northern regions for which not a scrap of evidence can be adduced, while they can give no proof of contemporaneous depression of the Isthmus of Panama. Next, relying on Mr. Jamieson's hypothesis, they take for granted that the ice-sheets, called into existence by their postulated earth-movements, succeeded in depressing the earth's surface even below its present level. That is to say, the land, which, according to them, was in glacial times some 3000 feet higher than now, sank down under the weight of its glacial covering for, say, 3600 feet in north-western Europe. In North America, in like manner, all the pre-glacial elevation was lost--the land sinking below its present level for some 200 feet in New England, for 520 feet at Montreal, for 1000 to 1500 feet in Labrador, and for