Page:The fairy tales of science.djvu/291

 These observations established the strange and unexpected conclusion, that the ice of glaciers, though apparently hard and brittle, can be bent and moulded under the enormous pressure of its own weight, and that instead of moving like an ordinary solid, it flows down the valley just as a viscous substance, such as partially melted pitch, would flow. Professor Forbes actually attributed this manner of motion to a slight degree of plasticity or a demi-semi-fluidity in the ice mass, and announced his new theory of glacier motion in these words:—"A glacier is an imperfect fluid, or a viscous body, which is urged down slopes of a certain inclination by the mutual pressure of its parts."

Our moving lands are thus robbed of their solidity, and become mere sluggish rivers of a marvellous sticky fluid, which we are unable to define with anything like accuracy,

But are we quite sure that the viscous theory is the only possible explanation of glacier motion? It is quite certain "that the manner of movement of the surface of a glacier coincides with the manner of motion of a viscous or semi-fluid body," but we have many reasons for doubting the viscosity of glacier ice. The yawning crevasses, the fantastic towers, and the perpetual crackling noise of a glacier, would seem to prove that it is formed of a very brittle material. But a substance cannot be brittle and viscous at the