Page:Canadian Alpine Journal I, 1.djvu/210

Rh times most beautifully polished and grooved by the ploughing over their surfaces of rocks and stones caught in the ice. Possibly the simile frequently used of the way in which thick mortar will run when poured out of a bucket gives as good an idea as any of the manner in which the ice composing a glacier flows. The region of transformation of snow into ice is called the névé.

There is still another and distinct apparent movement of glaciers, which is even more evident than that above described. Naturally when the ice stream reaches the lower and warmer altitudes, melting goes on more rapidly, until finally the end of the ice wastes away, and a stream or river ensues. Now, it is for only a very short time in each year, in the latitude that we are considering, that the temperature is such that the amount of daily melting of ice exactly corresponds with the daily advance produced by the flow of the glacier. Hence it is that we have an oscillation of the tongue, which in winter will gradually extend farther down the valley, whilst in summer it will gradually retreat. This same result of advance and retreat may also be produced by protracted changes of weather conditions as more or less precipitation, higher or lower mean annual temperature. Such must last, however, for terms of years in order to produce anything more than a temporary effect upon the glacier. This characteristic has long been noted, and it is found that usually through long cycles varying from a dozen up to thirty or more years, the glaciers of a given region will show each year a net advance and then again for a succeeding period successive annual recessions. Our Canadian glaciers are no exception to this rule, and during the time they have been observed retreat has been the almost universal movement.

Now, for a brief account of our personal observations on the various glaciers which we have studied: