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 the blade of a pocket-knife, and gradually widen according to the extent of the strain and the depth of the glacier. Now some of these cracks are interrupted, like the cracks in wood, and in opening, the strip of ice between overlapping ends is dragged out, and may maintain a continuous connection between the sides, just as the two sides of a slivered crack in wood that is being split are connected. Some crevasses remain open for months or even years, and by the melting of their sides continue to increase in width long after the opening strain has ceased; while the sliver-bridges, level on top at first and