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146 described in § 7. The highest points of the rocks are most affected, while the sides of depressions escape wholly, or partially, according as they are unopposed or opposed, to the direction of the motion of the glacier. Eminences are entirely removed in course of time", and their positions, and those of cracks or depressions, are only indicated by faintly-marked convexities and concavities (Fig. 4). These may at length disappear, and large areas of rock may be reduced to plane surfaces.

Such surfaces are common in Greenland, in close proximity to, and extending underneath, existing glaciers. I propose to call them roches nivelées, to distinguish them from roches moutonnées.

§ 9. Striations are frequently produced on rocks by the passage of glaciers (see illustration on ). They are caused by foreign matter in the bottoms of the glaciers, fixed in the ice, or rolling or sliding between it and the rocks. This foreign matter is partly made up of fragments which have been removed from the rock-bed by the action of the glacier, and partly from rocks which have fallen on to the surface of the glacier, and which have subsequently tumbled into crevasses, or otherwise worked their way down.

Generally speaking, striations are common upon rocks which are only 'moutonnées,' but they are rarer, or entirely wanting, upon