"At length our way was barred by a very wide and straight crevasse, which I traced rapidly northward a mile or so without finding a crossing or hope of one; then down the glacier about as far, to where it united with another uncrossable crevasse. In all this distance of perhaps two miles there was only one place where I could possibly jump it, but the width of this jump was the utmost I dared attempt, while the danger of slipping on the farther side was so great that I was loath to try it. Furthermore, the side I was on was about a foot higher than the other, and even with this advantage the crevasse seemed dangerously wide. One is liable to underestimate the width of crevasses where the magnitudes in general are great. I therefore stared at this one mighty keenly, estimating its width and the shape of the edge on the farther side, until I thought that I could jump it if necessary, but that in case I should be compelled to jump back from the lower side I might fail. Now, a cautious mountaineer seldom takes a step on unknown ground which seems at all dangerous that he cannot retrace in case he should be stopped by unseen obstacles ahead. This is the rule of mountaineers who live long, and, though in haste, I compelled myself to sit down and calmly deliberate before I broke it."