National Geographic : 1892 Mar 21
H. :F Reid-Studies of Muir Glacier. haps the tenth to the sixteenth centuries, the glaciers of the Alps were much less extensive than at present, and that horses were able to cross passes now considered difficult by mountaineers. During the seventeenth and eighteenth centuries the glaciers increased, attaining their greatest extent in the beginning of this century.* At present they are in general retreating. This shows a variation almost as great and almost as rapid as that mentioned for the glaciers of Glacier bay. A possible Cause of the recent Retreat. When the tide in Muir inlet is very low one can see on its eastern shore the stumps of large trees, which Professor Muir assures me are in place. The trees must have grown, of course, above high tide; they are now twenty feet below that level. Although I cannot say so with certainty, it is not unreasonable to suppose that these trees, like those of the buried forest, are spruce, and of the same species as those now growing in Alaska; but we must remember that any results deduced from this sup position have no more weight than the supposition itself. If, therefore, these trees were growing at the same time as those of the buried forest, there has been a subsidence of the land of at least 20 feet since the last advance of the glacier; it may have been much more; if so, it would have produced an increase in the mean annual temperature, which would have increased the rate of melting and would also have decreased the proportion of the solid to the liquid precipitation; and on account of the general lowering of the mountains, more of the moisture from the ocean may have been carried over them and precipitated further inland. All of these results would tend to diminish the extent of the glacier. Not only that, but the diminution itself would increase the rate of diminution, for the presence of extensive snow-fields must lower the mean annual temperature (see page 52) and thus increase the proportion of snow to the total pre cipitation. If for any cause these snow-fields become smaller, their influence on the mean temperature becomes less, the snow fall is diminished, and the snow-fields become smaller still. So we see that anything causing a slight change in the mean tem perature may result finally in quite a large variation in the ex tension of the glacier, although this large variation may reach its limit only long after the cause which started it has ceased to *Agassiz, Etudes sur les Glaciers, 1840, chap. xvi.
1892 May 15
1892 Feb 19