. Elements of geology : a text-book for colleges and for the general reader. Geology. 6i AQUEOUS AGENCIES. Regelation.—If two slabs of ice be laid one atop of the other, they soon freeze into a solid mass. This will take place not only in cold weather, but in midsummer, or even if boiling water be thrown over the slabs. If a mass of ice be broken to pieces, and the fragments be pressed or even brought in contact with one another, they will quickly unite into a solid mass. Snow pressed in the warm hand, though con- stantly melting, gradually becomes compacted into solid ice. This very remarkabl
. Elements of geology : a text-book for colleges and for the general reader. Geology. 6i AQUEOUS AGENCIES. Regelation.—If two slabs of ice be laid one atop of the other, they soon freeze into a solid mass. This will take place not only in cold weather, but in midsummer, or even if boiling water be thrown over the slabs. If a mass of ice be broken to pieces, and the fragments be pressed or even brought in contact with one another, they will quickly unite into a solid mass. Snow pressed in the warm hand, though con- stantly melting, gradually becomes compacted into solid ice. This very remarkable but imperfectly understood property of ice completely ex- plains the phenomena of molding ice by experiment. By this property the broken fragments reunite in a new form as solid as before. We may possibly call this property of molding under pressure plasticity (although it is not true plasticity, since it does not mold without rupt- ure, but by rupture and regelation); but it can not in any sense be called viscosity, for the true definition of viscosity is the property of yielding under tension — the property of stretching like molasses-candy, or melted glass; but ice in the experiments, according to Tyndall, did not yield in the slightest degree to tension. In the experiment, if, instead of placing the straight bar at once into the curved mold, it had been placed successively in a thousand molds, with gradually-increased curvature, or, still better, if placed in a straight mold, and this mold, while under pressure, curved slowly, then there would have been no sudden visible ruptures, but an infinite number of small ruptures and regelations going on all the time. The ice ivould have behaved precise- ly like a viscous body. Xow, this is precisely what takes place in a glacier. Application to Glaciers.—A glacier, on account of its immense mass, is, in its loicer parts, under the heavy pressure of its own weight tending to mold it to the inequalities of its own bed, and in
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