72 REPORT OF THE SECRETARY. 



his administrative report for the year 188G he gives a sutiimarizetl state- 

 ment of the results which have been reached by the studies in which 

 he and his associates have been engaged. 



Among these the following may be mentioned : (1) Tlie origin of the 

 ferruginous schists of the Lake Superior region and their accompany- 

 ing iron ores is attributable to the silicification of ferruginous carbon- 

 ates in some degree analogous to those of the coal-measures. (2) The 

 Archean formations of Lake Superior are divisible into two discordant 

 members, to which the terms Huronian and Laurentian should be ap- 

 plied. (3) Such chloritic schists as present themselves at the falls of 

 the Menomonee River, on the boundary between Wisconsin and Michi- 

 gan, are the result of metasomatic alteration, accompanying great press- 

 ure, of some sort of eruptive greenstone. (4) The upper mica schists 

 of the iron-bearing series have been developed in both the Penokee and 

 the Marquette regions from entirely fragmental rocks, composed mainly 

 of quartz and feldspar, by a simple, easily traced process of metaso- 

 matosis. 



Division of Glacial Geology. — Prof. T. C. Chambei-lin and his assist- 

 ants. Prof. R. D. Salisbury, Prof. J. E. Todd, Mr. Warren Upham, Prof. 

 G. H. Stone, Prof. G. F. Wright, and Mr. L M. Bueli, were engaged in a 

 comprehensive study of the manifold features of glacial geology, par- 

 ticularly as recorded in the rocks of the northwestern se'ction of the 

 United States. To the discussion of this question. Professor Chamberlin 

 has contributed two extended articles, one appearing in the Sixth An- 

 nual Report, under the heading of the "Driftless Area of the United 

 States," and the other in the seventh, under the title of the "Rock Scor- 

 ings of the Great Ice Invasion." His assistant, Mr. Upham, after making 

 an extended investigation of the area of the extinct lake (Agassiz), 

 submitted the manuscript for a bulletin, which will appear among the 

 publications of the Survey hereafter. In company with Prof. Salisbury, 

 Prof. Chamberlin undertook a reconnoissance of the drift margin from 

 the vicinity of Bismarck, Dak., to the national boundary line at the foot 

 of the Rocky Mountains. No attempt was made to trace the drift-border 

 in detail, but it was sought to determine a sufficient number of points 

 to fix beyond question the general course and character of the drift 

 in Northwestern Dakota and in Montana. After about a month spent 

 in this examination, Prof. Chamberlin studied the valley-drift of the 

 Yellowstone River, at Billings, and in the vicinity of Glendive, with 

 a view to distinguishing this semi-local drift from that of the north- 

 east^ as well as to determining the ancient fluvial conditions of the re- 

 gion. He also spent about a month in the study of drift phenomena 

 in Montana, Idaho, and British Columbia. Professor Todd's time was 

 devoted to field study in southern Dakota, and the preparation of a 

 bulletin on his results. Professor Stone, under the direction of Prof. 

 Chamberlin, continued his special investigations of the gravels of 



