74 REPORT OF THE SECRETARY. 



source in the great ne" ve" of the Sierra Nevada. Within the area of that 

 neve are a number of small modern glaciers which were included in the 

 investigation. 



Messrs. Gilbert and Eussell have devoted the time not consumed by 

 field-work to the preparation of reports, preliminary and final, on the 

 Quaternary lakes. The final reports will include monographs on Lake 

 Bonneville, Lake Lahontan, and the Mono Basin. 



Study of Metamorphic rocks. — Prof. R. D. Irving had five parties in the 

 field continuing the investigation of the copper-bearing rocks. The 

 examination of the Huronian rocks, in the vicinity of Sault Ste. Marie, 

 Mich., was completed, and the field of investigation was extended north 

 of Lake Superior to the National boundary, and along the latter west- 

 ward to Rove Lake, Michigan. Special investigations were made in the 

 vicinity of Sault Ste. Marie and at various other points in the neighbor- 

 hood of Lake Superior. A study was made of the crystalline rocks of 

 Morrison and Todd Counties, Minnesota, and a study of the Huronian 

 quartzites of the Minnesota Valley. Professor Todd's report on the 

 " Copper-bearing Rocks" is in type and awaiting the completion of the 

 illustrations before publication. Early in September the Animikie group 

 was examined along a route which gave two complete sections of the 

 series from the junction with the Keweenawan, on the islands near 

 Pigeon Point, along the boundary line to the underlying granite of 

 Sanaga Lake, and along the west side of Thunder Bay to Port Arthur. 

 The examination of the Minnesota Valley, begun in the latter part of 

 August, was continued until the middle of September, when field work 

 was stopped for the season. Considerable microscopic work has been 

 done by Professor Todd and his assistants. Since the beginning of their 

 study of the metamorphic rocks in 1882 thin sections of 500 rocks have 

 been made, of which number written descriptions of 300 have been pre- 

 pared. They include tfocks from the original Huronian, the Huronian 

 of the Marquette and Menominee regions, the Animikie group of the 

 National boundary, the folded schists of the same region, and the crys- 

 talline rocks of the Minnesota and Mississippi Valleys. Professor Irving, 

 in October, made a personal examination of the quartzites of Nicollet 

 and Cottonwood Counties, Minnesota. A comparative study of the 

 greenstones, etc., of Huronian age will be carried on. Office work has 

 developed some interesting results in relation to the structure of the 

 quartzites of the Huronian of Lake Huron and of the Marquette and 

 concerning their relations to each other. 



Yellowstone and Missouri Rivers. — The region between the Missouri 

 River at Bismarck, Dak., and the Yellowstone Valley at Glendive, 

 Mont., and along the Yellowstone River from Glendive to Livingston, 

 Mont., with a portion of Montana in the vicinity of Bozemau, was the 

 field of a geological reconnaissance by Dr. F. V. Hayden, who was 

 assisted by Dr. A. C. Peale. Sections were made at various points along 

 the line of the Northern Pacific Railroad with especial relation to the 



