F. GEOGRAPHY. 261 



so recently that the Bonneville flood is ancient in compari- 

 son. 



Captain C. E. Button resumed this year his study of the 

 large area of igneous rocks in Southern Utah, in the vicinity 

 of the Sevier River, and has brought back additional infor- 

 mation, which he purposes employing in the preparation of a 

 monograph of the entire track. He has worked out the struct- 

 ure of the component features and the approximate age of 

 the eruptions, and is engaged in classifying the various lith- 

 ologic members. The older outbreaks appear to be of early 

 tertiary age (eocene), and to have been nearly continuous 

 through a long period. The volcanic beds thus formed were 

 subsequently traversed by great flxults, and tables were up- 

 lifted with deep valleys between them ; the structure thus 

 produced conforming to the general type prevalent through- 

 out the plateau country. The degradation of these lofty 

 tables gave rise to conglomerate beds of great extent and 

 thickness, which are composed entirely of volcanic materials. 

 Captain Dutton has compared the details and arrangement 

 of these cono-lomerates with the alluvial beds now accumu- 

 lating 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 under- 

 lying sedimentary beds (early tertiary), but in the super- 

 posed conglomerate, and which he thinks must have occurred 

 comparatively near the surfjice. The greater portion by far 

 of the erupted rocks he classes as trachytes and trachy-dole- 

 rites. Tiie rhyolitic varieties are of very limited occurrence, 

 being found only in the vicinity of the Beaver or Tushar 

 Range. In the southwestern part of the field (near Sang- 

 quitch) extensive fields of basalt are found. Captain Dut- 

 ton 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 properly 

 dolerite or anamesite, the latter typical basalt. 



Under instructions from the Interior Department, Profess- 

 or 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 w^as the classification 

 of the Indian tribes, such classification being not only of 



