Chapter XVIII. My Sled-Trip on the Muir Glacier
I have gained some light on the formation of gravel-beds along the inlet. The material is mostly sifted and sorted by successive railings and washings along the margins of the glacier-tributaries, where the supply is abundant beyond anything I ever saw elsewhere. The lowering of the surface of a glacier when its walls are not too steep leaves a part of the margin dead and buried and protected from the wasting sunshine beneath the lateral moraines. Thus a marginal valley is formed, clear ice on one side, or nearly so, buried ice on the other. As melting goes on, the marginal trough, or valley, grows deeper and wider, since both sides are being melted, the land side slower. The dead, protected ice in melting first sheds off the large boulders, as they are not able to lie on slopes where smaller ones can. Then the next larger ones are rolled off, and pebbles and sand in succession. Meanwhile this material is subjected to torrent-action, as if it were cast into a trough. When floods come it is carried forward and stratified, according to the force of the current, sand, mud, or larger material. This exposes fresh surfaces of ice and melting goes on again, until enough material has been undermined to form a veil in front; then follows another washing and carrying-away and depositing where the current is allowed to spread. In melting, protected margin terraces are oftentimes formed. Perhaps these terraces mark successive heights of the glacial surface. From terrace to terrace the grist of stone is rolled and sifted. Some, meeting only feeble streams, have only the fine particles carried away and deposited in smooth beds; others, coarser, from swifter streams, overspread the fine beds, while many of the large boulders no doubt roll back upon the glacier to go on their travels again.
It has been cloudy mostly to-day, though sunny in the afternoon, and my eyes are getting better. The steamer Queen is expected in a day or two, so I must try to get down to the inlet to-morrow and make signal to have some of the Reid party ferry me over. I must hear from home, write letters, get rest and more to eat.
Near the front of the glacier the ice was perfectly free, apparently, of anything like a crevasse, and in walking almost carelessly down it I stopped opposite the large granite Nunatak Island, thinking that I would there be partly sheltered from the wind. I had not gone a dozen steps toward the island when I suddenly dropped into a concealed water-filled crevasse, which on the surface showed not the slightest sign of its existence. This crevasse like many others was being used as the channel of a stream, and at some narrow point the small cubical masses of ice into which the glacier surface disintegrates were jammed and extended back farther and farther till they completely covered and concealed the water. Into this I suddenly plunged, after crossing thousands of really dangerous crevasses, but never before had I encountered a danger so completely concealed. Down I plunged over head and ears, but of course bobbed up again, and after a hard struggle succeeded in dragging myself out over the farther side. Then I pulled my sled over close to Nunatak cliff, made haste to strip off my clothing, threw it in a sloppy heap and crept into my sleeping-bag to shiver away the night as best I could.
July 21. Dressing this rainy morning was a miserable job, but might have been worse. After wringing my sloppy underclothing, getting it on was far from pleasant. My eyes are better and I feel no bad effect from my icy bath. The last trace of my three months' cough is gone. No lowland grippe microbe could survive such experiences.
I have had a fine telling day examining the ruins of the old forest of Sitka spruce that no great time ago grew in a shallow mud-filled basin near the southwest corner of the glacier. The trees were protected by a spur of the mountain that puts out here, and when the glacier advanced they were simply flooded with fine sand and overborne. Stumps by the hundred, three to fifteen feet high, rooted in a stream of fine blue mud on cobbles, still have their bark on. A stratum of decomposed bark, leaves, cones, and old trunks is still in place. Some of the stumps are on rocky ridges of gravelly soil about one hundred and twenty-five feet above the sea. The valley has been washed out by the stream now occupying it, one of the glacier's draining streams a mile long or more and an eighth of a mile wide.
I got supper early and was just going to bed, when I was startled by seeing a man coming across the moraine, Professor Reid, who had seen me from the main camp and who came with Mr. Loomis and the cook in their boat to ferry me over. I had not intended making signals for them until to-morrow but was glad to go. I had been seen also by Mr. Case and one of his companions, who were on the western mountain-side above the fossil forest, shooting ptarmigans. I had a good rest and sleep and leisure to find out how rich I was in new facts and pictures and how tired and hungry I was.