Page:The Journal of geology (IA journalofgeology21894univers).pdf/138
An estimate of the volume of rock matter which is carried by the glacial rivers of Greenland and Norway proves also that the glacier denudation in a few thousand years must reach great dimensions.
When thus the capacity of the rock basins comes short of holding the known glacial sediment (the quantitative element), the form of the basins (the qualitative element) is quite in harmony with those we find in other glaciated countries and nowhere else. Both the lakes and the fjords have a distinguishing trough shape, with flat bottoms and comparatively steep sides, in the transverse section, and, in the longitudinal section, a gradual deepening toward a point that is situated not very far from the outer end, against which it more suddenly shoals up. This form cannot be generated by any other possible eroding agent than glacier ice. The fissure theory is out of the question, as exact sections specifically show. Faults and dislocations cannot account for their specific form and their relations to quite superficial topographical features. The admirable monograph on the Kristiania fjord, by Professor W. C. Brögger, makes it also quite clear that its distinguishing fjord character can only be of glacial origin. Basins of this form, as is well known, are restricted to glaciated countries; and they can be deduced directly from the motion of the eroding glacier. The movement must accelerate towards the point where the ice surface intersects the snow line, where the surplus ice from the whole glacier must pass. Thence it must slacken because of the melting farther down. The erosion, which naturally must depend both on the movement and the pressure of the ice, will decrease accordingly. In this we find the explanation both of the longitudinal form of the glacial basins, and of their evident dependence on the margin of the land ice.
So much may be said about glacial erosion by way of introduction before entering into the study of the succession of glacial events in Norway. We must be somewhat prepared to face the greatness of the phenomena, which only glacial studies can make more familiar to us.
When we try to realize the appearance of Norway in pre-