Page:The Journal of geology (IA journalofgeology21894univers).pdf/147

way in epiglacial time was very like a modern map of Greenland. The isotherm of 0°C. for the year must have followed the southern coast perhaps as far up as to the polar circle. The lower isotherms must have enclosed a pronounced minimum to the east of the ice shed, where certainly — 20°C. must have reigned.^[1] While the difference from the present mean temperature at the coast was only 5 to 6° C., the difference near the pole of maximum cold most have been 15° C. at least. This great difference, which is a necessary consequence of the contrast between coast climate and the pronounced continental climate over the east side of the great ice field, is as yet not sufficiently noted by the students of glacial time. An exact consideration of the distribution of the meteorological elements above the inland ices will give the solution of many glacial problems. I shall here only remark that the snowfall in this continental region must have been almost imperceptible as in winter in Sibera now—and likewise the melting. Now, the power which keeps the glacier in motion is ever the surplus of snowfall. The whole continental side of the inland ice must thus be kept in quite a passive motion, be pushed as a rather thin ice plate out to the margin by the press from the greater snowfall on inside ice nearer the ice shed and the coast. The reliable measures of the ice sheet in the Baltic show really very small dimensions—less than 200 meters—thus it will become intelligible why the greater ice masses to the west can keep the ice divide four to six times nearer the western margin. An ice plate of about 100 meters or less must be impotent to erode. The bottom moraine from the more powerful inner part must be gradually built up below the outer thin marginal ice sheet. On the continental side we will have formed a regular boulder-clay or thick bottom moraine outside an area where denudation in the form of broad shallow basins or plains will still take place—all this against the deep rock basins with terminal moraines and terraces before them, on the coast side. The snowfall here will be very great. The surplus ice