Some of the rocks which lay upon the glacier were very large, several of them being as big as houses. It was remarkable, too, that the largest of them, instead of having settled down in some degree into the ice and snow, as it might have been expected from their great weight they would have done, were raised sometimes many feet above the general level of the glacier, being mounted on a sort of pedestal of ice. The reason of this was, that when the block was very large, so large that the beams of the sun shining upon it all day would not warm it through, then the ice beneath it would be protected by its coolness, while the surface of the glacier around would be gradually melted and wasted away by the beams of the sun or by the warm rains which might occasionally fall upon it. Thus, in process of time, the great bowlder block rises, as it were, many feet into the air, and remains there perched on the top of a little hillock of ice, like a mass of monumental marble on a pedestal.[14] In excursions on the glaciers the guides take a rope with them, and sometimes a light ladder. The rope is for various purposes. If a traveller were to fall into any deep pit, or crevasse, or to slip down some steep slope or precipice, so that he could not get up again, the guides might let the rope down to him, and then when he had fastened it around his waist they could draw him up, when, without some such means of rescuing him, he would be wholly lost. In the same manner, when a party are walking along any very steep and slippery place, where if any one were to fall he would slide down into some dreadful abyss, it is customary for them to walk in a line with the rope in their hands, each one taking hold of it. Thus, if any one should slip a little, he could recover himself by means of the rope, when, without such a support, he would perhaps have fallen and been dashed to pieces. Sometimes, when the place is very dangerous indeed, so that several guides are required to each traveller, they tie the rope round the traveller's waist, so that he can have his hands free and yet avail himself of the support of the rope in passing along. The ladder is used for scaling low precipices, either of rock or ice, which sometimes come in the way, and which could not be surmounted without such aid. In long and dangerous excursions, especially among the higher Alps, one of the guides always carries a ladder; and there are frequent occasions where it would not be possible to go on without using it. [Illustration: ASCENT OF MONT BLANC.]