If I got my feet on the rock the effort would bring me too far into the water, and that meant destruction.

I saw this clearly in a second while my wrists were cracking with the strain.

But if I had a wall behind me I could reach back with one hand and get what we call in Scotland a 'stelf.' I knew there was a wall, but how far I could not judge.

The perpetual hammering of the stream had confused my wits.
It was a horrible moment, but I had to risk it.

I knew that if the wall was too far back I should fall, for I had to let my weight go till my hand fell on it.