At the turning, the ledge got narrow, and one must seize a knob and then step lightly on a stone embedded in mossy soil.
When they reached the spot Hyslop stopped and told Vernon what to do; the girl immediately behind him was a clever mountaineer.

They went round and Lister watched from a few yards off.

For a moment or two each in turn, supported by one foot with body braced against the rock, grasped the knob and vanished round the corner.

It was plain one must get a firm hold, but Lister thought this was all.

He was used to the tall skeleton trestles that carried the rails across Canadian ravines.
After the others disappeared Lister seized the knob.