Johnson himself called attention to the slender basis of observation upon which his conclusions rest. In spite of his own caution with respect to the use of his meager data, his hypothesis has been applied in an entirely too confident manner to all kinds of cirques under all kinds of conditions. Though Johnson descended an open bergschrund to a rock floor upon which ice rested, his observations raise a number of proper questions as to the application of these valuable data: How long are bergschrunds open? How often are they open? Do they everywhere open to the foot of the cirque wall? Are they present for even a part of the year in all well-developed cirques? Let us suppose that it is possible to find many cirques filled with snow, not ice, surrounded by truly precipitous walls and with an absence of bergschrunds, how shall we explain the topographic depressions excavated underneath the snow? If cirque formation can be shown to take place without concentrated frost action at the foot of the bergschrund, then is the bergschrund not a secondary rather than a primary factor? And must we not further conclude that when present it but hastens an action which is common to all snow-covered recesses?
It is a pleasure to say that we may soon have a restatement of the cirque problem from the father of the bergschrund idea. The argument in this chapter was presented orally to him after he had remarked that he was glad to know that some one was finding fault with his hypothesis. “For,” he said, with admirable spirit, “I am about to make a most violent attack upon the so-called Johnson hypothesis.” I wish to say frankly that while he regards the following argument as a valid addition to the problem, he does not think that it solves the problem. There are many of us who will read his new explanation with the deepest interest.
Fig. 196—Relation of cirque wall to trough’s end at the head of a glaciated valley. The ratio of the inner to the outer radius is 1:4.