On our right the glacier torrent thundered down the valley through a gorge with precipitous sides, not easily approached, for the turf at the top was slippery, and the rocks had everywhere been rounded by the glacier, which formerly extended far away. This gorge seems to have been made chiefly by the torrent, and to have been excavated subsequently to the retreat of the glacier. It seems so, because not merely upon its walls are there the marks of running water, but even upon the rounded rocks at the top of its walls, at a height of seventy or eighty feet above the present level of the torrent, there are some of those queer concavities which rapid streams alone are known to produce on rocks.
A little bridge, apparently frail, spans the torrent just above the entrance to this gorge, and from it one perceives being fashioned in the rocks below concavities similar to those to which reference has just been made. The torrent is seen hurrying forward. Not everywhere. In some places the water strikes projecting angles, and, thrown back by them, remains almost stationary, eddying round and round: in others, obstructions fling it up in fountains, which play perpetually on the under surfaces of overhanging masses; and sometimes do so in such a way that the water not only works upon the under surfaces, but round the corner; that is to say, upon the surfaces which are not opposed to the general direction of the current. In all cases concavities are being produced. Projecting angles are rounded, it is true, and are more or less convex, but they are overlooked on account of the prevalence of concave forms.
WATER-WORN ROCKS IN THE GORGE BELOW THE GÖRNER GLACIER
Cause and effect help each other here. The inequalities of the torrent bed and walls cause its eddyings, and the eddies fashion the concavities. The more profound the latter become, the more disturbance is caused in the water. The destruction of the rocks proceeds at an ever-increasing rate, for the larger the amount of surface that is exposed, the greater are the opportunities for the assaults of heat and cold.
When water is in the form of glacier it has not the power of making concavities such as these in rocks, and of working upon surfaces which are not opposed to the direction of the current. Its nature is changed: it operates in a different way, and it leaves marks which are readily distinguished from those produced by torrent action.
STRIATIONS PRODUCED BY GLACIER ACTION (AT GRINDELWALD)