The breadth of the groove is often not more than from forty to sixty yards, and it has some sharp turnings, double channels, and little cataracts in it.

As we steamed up, the masts of the "Ma Robert," though some thirty feet high, did not reach the level of the flood-channel above, and the man in the chains sung out, "No bottom at ten fathoms." Huge pot-holes, as large as draw-wells, had been worn in the sides, and were so deep that in some instances, when protected from the sun by overhanging boulders, the water in them was quite cool.

Some of these holes had been worn right through, and only the side next the rock remained; while the sides of the groove of the flood-channel were polished as smooth as if they had gone through the granite-mills of Aberdeen.

The pressure of the water must be enormous to produce this polish.

It had wedged round pebbles into chinks and crannies of the rocks so firmly that, though they looked quite loose, they could not be moved except with a hammer.