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Historical Note.—This paper was presented before the American Association for the Advancement of Science at the Minneapolis meeting, where it was kindly read by Mr. Warren Upham in the absence of the author. A brief abstract was printed in the proceedings of that body for 1883, page 238. Subsequently, Dr. J. E. Hendricks, long editor of The Analyst, did the favor of reviewing the mathematical portions, and his suggestions are embodied in a note.

The paper is the fruit of field studies in the Sierra Nevada, mainly in the region about Lake Mono, and of subsequent office work in Salt Lake City, under the direction of I. C. Russell, then of the United States Geological Survey, in 1882 and 1883. The paper was not published because it was recognized that one of the most important phases of ice work (i. e., the work at the bottom of the Bergschrund involved in the formation of cirques and rock basins) was not adequately treated. It was then, as it is now, the opinion of the author that ice work is concentrated and culminates in effectiveness in cirques, whether at the heads of water-carved tributaries (cyms or coombes) or in amphitheatres below ice-falls due to varigradational irregularities in the antecedent water-cut profiles, and that this concentration is proved and the correct analyses of the process suggested by the Bergsschrund in the one case and by seracs in the other; but the analysis is difficult, and neither then nor later have opportunities occurred for working it out. Recently this phase of ice work has been taken up by Mr. Willard D. Johnson, who brings to the work a rich fund of observation and an acute and vigorous mind, while at the same time the author finds the promise for the desired opportunity for further study fading away; so it is deemed best to publish in the present form, leaving extension and application to others. It may be observed that, while the treatment