62 REPORT OF THE SECRETARY. 



and has brought back additional information which he purposes em- 

 ploying in the preparation of a monograph of the entire tract. He has 

 worked out the structure of the component features, and the approxi- 

 mate area of the eruptions, and is engaged in classifying the various 

 lithologic members. The older outbreaks appear to be of early Tertian 

 age, (Eocene,) and to have been nearly continuous through a long 

 period. The volcanic beds thus formed were subsequently traversed by 

 great faults, and tables were uplifted, with deep valleys between them; 

 the structure thus produced conforming to the general type prevalent 

 throughout the plateau country. The degradation of these long lofty 

 tables gave rise to conglomerate beds of great extent and thickness, 

 which are composed entirely of volcauic materials. Captain Button 

 has compared the details and arrangement of these conglomerates with 

 the alluvial beds now accumulating in great volume in the valleys out 

 of the waste of the adjoining tables, and finds an agreement between 

 them so close that he ascribes the same mode of origin to both. He 

 also finds considerable metamorphism not only in the underlying sed- 

 imentary beds (early Tertiary) but in the superposed conglomerate; 

 and he thinks it must have occurred comparatively near the surface. 

 The greater portion by far of the erupted rocks he classes as trachytes 

 and trachydolerites. The rhyolitic varieties are of very limited occur- 

 rence, being found only in the vicinity of the Beaver or Tunbar Range. 

 In the southwestern part of the field (near Pauguitch) extensive fields 

 of basalt are found. Captain Duttou distinguishes two ages of the 

 basalt; one prior to the development of the present structural features 

 of the region, the other subsequent to it — the former being more prop- 

 erly dolerite or anamesite, the latter typical basalt. 



Under instructions from the Interior Department, Professor Powell 

 and his parties have also been engaged in general ethnographic work 

 in the Rocky Mountain Region. One of the special items in these 

 instructions was the classification of the Indian tribes, such classification 

 being not only of scientific interest, but of great importance in the 

 administration of Indian affairs. For the eastern portion of the United 

 States this w»rk had been accomplished — first by the unofficial labors 

 of the Hon. Albert Gallatin, and subsequently by the Hon. Henry R. 

 Schoolcraft, as an officer of the Government ; and some addition had 

 been made to the work by various persons for scientific purposes. 

 This work has been renewed by Professor Powell, and has been pushed 

 with all the energy possible with the funds at his command, and a 

 large amount of material has been collected by himself and by members 

 of his corps, and by residents in and travelers through the country. 

 In addition to this a large amount had been collected by the Smith- 

 sonian Institution through various channels — materials as yet unpub- 

 lished. That Institution has placed all this matter in the hands 

 of Professor Powell to be combined with his own collections. The first 

 volume of the reports on this subject will soon be issued. It treats of 



