The mountain-side was too steep for him to stand upright, except at moments.

It seemed one uniform quarry of smooth broken slate, slipping down for ever beneath his feet .-- Whither?
He grew giddy, and more giddy; and a horrible fantastic notion seized him, that he had lost his way; that somehow, the precipice had no bottom, no end at all; that he was going down some infinite abyss, into the very depths of the earth, and the molten roots of the mountains, never to reascend.
He stopped, trembling, only to slide down again; terrified, he tried to struggle upward: but the shale gave way beneath his feet, and go he must.
What was that noise above his head?
A falling stone?
Were his enemies in pursuit?
Down to the depth of hell rather than that they should take him! He drove his heels into the slippery shale, and rushed forward blindly, springing, slipping, falling, rolling, till he stopped breathless on a jutting slab.

And lo! below him, through the thin pearly veil of cloud, a dim world of dark cliffs, blue lakes, grey mountains with their dark heads wrapped in cloud, and the straight vale of Nant Francon, magnified in mist, till it seemed to stretch for hundreds of leagues towards the rosy north-east dawning and the shining sea.
With a wild shout he hurried onward.

In five minutes he was clear of the cloud.

He reached the foot of that enormous slope, and hurried over rocky ways, till he stopped at the top of a precipice, full six hundred feet above the lonely tarn of Idwal.
Never mind.