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It was intended that Mr. Kerr's report, forming Appendix B, should contain a detailed record of the triangulation executed last summer, but a careful revision of his work by a committee of the National Geographic Society led to the conclusion that the results were not of sufficient accuracy to set at rest the questions raised by the discrepancies in earlier measurements of the height of Mount St. Elias; and as the work will probably be revised and extended during the summer of 1891, only the map forming plate 8 will be published at this time. Some preliminary publications of elevations have been made, but these must be taken as approximations merely.*
By consulting the map forming plate 8 it will be seen that Mounts Cook, Vancouver, Irving, Owen, etc., are not in the St. Elias range. Neither do they form a distinct range either topographically or geologically. Each of these mountains is an independent uplift, although they may have some structural connection, and are of about the same geological age. Mount Cook and the peaks most intimately associated with it are composed mainly of sandstone and shale belonging to the Yakutat system. Mounts Vancouver and Irving are probably of the same character, but definite proof that this is the case has not been obtained.
The St. Elias uplift is distinct and well marked, both geologically and topographically, and deserves to be considered as a mountain range. The limits of the range have not been determined, but, so far as known, its maximum elevation is at Mount St. Elias. The range stretches away from this culminating point both northeastward and northwestward, and has a well-marked V-shape. The angle formed by the two branches of the range where they unite at Mount St. Elias is, by estimate, about 140°. Each arm of the V is determined by a fault, or perhaps more accurately by a series of faults having the same general course, along which the orographic blocks forming the range have been upheaved. The structure of the range is monoclinal, and re
* The shore-line of the map, plate 8, and the positions of the initial points or base-line of the triangulation are from the work of the United States Coast Survey. The extreme western portion is from maps published by the New York Times and Topham expeditions. All the topographic data are by Mr. Kerr, and all credit for the work and all responsibility for its accuray rest with him. The nomenclature is principally my own, and has been approved by il committee of the National Geographic Society.
sembles the type of mountain structure characteristic of the great basin. The dip of the tilted blocks is northward.
The crest of the St. Elias range, as already stated, is composed of schists which rest on sandstone, supposed to belong to the Yakutat system. The geological age of the uplift is, therefore, very recent. The secondary topographic forms on the crest of the range have resulted from the weathering of the upturned edges of orographic blocks in which the bedding planes are crossed by joints. The resulting forms are mainly pyramids and roof-like ridges with triangular gables. Extreme ruggedness and angularity characterize the range throughout. There are no rounded domes or smoothed and polished surfaces to suggest that the higher summits have ever been subjected to general glacial action; neither is there any evidence of marked rock decay. Disintegration of all the higher peaks and crests is rapid, owing principally to great changes of temperature and the freezing of water in the interstices of the rock; but the débris resulting from this action is rapidly carried away by avalanches and glaciers, so that the crests as well as the subordinate features in the sculpture of the cliffs and pyramids are all angular. The subdued and rounded contour, due to the accumulation of the products of disintegration and decay, the indications of the advancing age of mountains, are nowhere to be seen. The St. Elias range is young; probably the very youngest of the important mountain ranges on this continent. No evidences of erosion previous to the formation of the ice-sheets that now clothe it have been observed. Glaciers apparently took immediate possession of the lines of depression as the mountain range grew in height, and furnish a living example from which to determine the part that ice streams play in mountain sculpture.
OFFICIAL INSTRUCTIONS GOVERNING THE EXPEDITION.
In order to make the records of the St. Elias expedition complete, copies of the instructions under which the work was carried out are appended :
DEPARTMENT OF THE INTERIOR,
Washington, D. C., May 28, 1890. Mr. I. C. RUSSELL, Geologist.
Sir: You are hereby detailed to visit the St. Elias range of Alaska for work of exploration, under the joint auspices of the National Geographic Society and the United States Geological Survey. The Geological Survey furnishes instruments and contributes the sum of $1,000 towards the expenses of the expedition. The money devoted to this purpose is taken from the appropriation for the fiscal year ending June 30, 1890, and the manner of its expenditure must conform to that fact.
The Survey expects that you will give special attention to glaciers, to their distribution, to the associated topographic types, to indications of the former extent of glaciation, and to types of subaërial sculpture under special conditions of erosion, and that you will also bring back information with reference to the age of the formations seen and the type of structure of the range.
With the aid of Mr. Kerr, it is expected that you will secure definite geographic information as to the belt of country traversed by you. Very respectfully,
G. K. GILBERT,
Chief Geologist. 1pproved,
J. W. POWELL, Director.
DEPARTMENT OF THE INTERIOR,
Washington, D. C., May 28, 1890. Mr. I. C. Russell, Geologist.
Sir: You will proceed at the earliest practicable date to Tacoma, Washington Territory, and thence by water to Sitka, Alaska, at which point you will make special arrangements to visit the St. Elias range of mountains and make geological examinations as per instructions otherwise communicated. Mr. Mark B. Kerr, Disbursing Agent, will report to you at Victoria, B. C., and accompany you on the expedition, assisting you in the capacities of Disbursing Agent and Topographer. On the completion of