Report of the Chief of Engineers U.S. Army

raphy on both sides of the river had been completed to the foot of St. Joseph Island, including that of the south shore of this island as far eastward as Grande Point. The topography of several of the islands in the northern half of Potagannissing Bay had also been obtained. The hydrography of the river had been finished to Detour Lumber Company's dock at Detour, by the ice survey in March, 1896.

During the past season the secondary and tertiary triangulation for controlling the topography and hydrography of Potagannissing Bay described in Mr. von Schon's last year's report, was extended by the addition of 2 quadrilaterals to the secondary system and 31 quadrilaterals to the tertiary system, covering completely the area surveyed.

The topography of all the islands lying in Potagannissing Bay, that of the shore line of Drummond Island from Poe Point on the north shore, westward around through Detour Passage and along the south shore to and including Whitney Bay was obtained. Also the topography of the right bank of the river from the point where the work of the previous year ended (before mentioned) down to the mouth of the river and a short distance westward along the Lake Huron shore.

In hydrographic work Potagannissing Bay and Detour Passage from Detour Lumber Company's dock to the mouth of the river were sounded.

The precise levels run during the season were the completion of the projected line from Sault Ste. Marie to Detour Light House, the part run being from T. B. M. No. 8, about 3 miles south of the Big Munuscong River to Detour Light, a distance of 35 miles.

The topography and hydrography are plotted on field or plane table sheets that are 22 by 25 inches in size. The work of the past season overlapped on 10 of the sheets of the year previous and required 19 new sheets. Tracings are made on vellum of these field sheets that are 25 by 45 inches in size. These tracings are called record-sheet tracings. The work of the season overlaps on 2 record sheets of last season and furnishes 9 new sheets.

The office work of reducing the notes of the secondary and tertiary triangulation on the preliminary computation of the line of precise levels were completed at the time the work was assigned to me. The field notes of the topography and hydrography were also about nine-tenths plotted.

The progress made since March 15 has been the completion of the plotting of the topographic and hydrographic notes, thus completing all of the plane-table sheets. Record sheets No. 29, Milford Haven; No. 30, Serpent; No. 31, Sulphur Island Light, have been made, leaving record sheets No. 32. Chippewa; No. 33, Potagannissing; No. 34, Maud Bay; No. 35, Detour; and No. 36, Detour Passage, to be drawn in order to complete the work.

The press of other work has prevented the checking of the computations of the precise level line, and the results from this work can not, therefore, be given at this writing.

There were associated with Mr. Von Schon as his assistants, Recorders Andrew J. Swift and Howard N. Eavenson; and also Rodmen Murray Blanchard and Charles E. Thompson, who assisted at instrument work in the field. Mr. Eavenson ran the line of precise levels and also made the preliminary computations of them. He resigned his position February 9, 1897, since when Mr. Swift has been the only assistant engaged upon the topographical work. Mr. Swift has also made, in connection with his regular work, most of the sketches for our annual reports. Tables Nos. 1, 2, 3, and 4, giving the results of the secondary and tertiary triangulation in Potagannissing Bay, are hereto appended.

Very respectfully, your obedient servant,

Mr. E. S. WHEELER, Assistant Engineer.

E. E. HASKELL, Assistant Engineer.