APPEiNDIX TO REPORT OF THE SECRETARY. 77 



the crust and formed subterranean lakes or chambers. The strata lying 

 above the lava lakes were upbent in the form of great bubbles, and from 

 these babbles of sandstone and shale, with their cores of trap, the erosive 

 agents of the air have carved the mountains. The mountain structure 

 is thus two-fold, comprising first volcanic upheaval, and second atmos- 

 pheric degradation. To aid in the discussion of the first element of 

 structure, Mr. Gilbert constructed a stereogram of the district, in 

 plaster, exhibiting the forms due to upheaval as they would appear if 

 unmodified by degradation. He prepared also a topographical model, 

 exhibiting the same forms as actually modified; and the two models 

 will be reproduced by photography to illustrate the report. The treat- 

 ment of the second element of structure is of a thorough character and 

 includes a discussion of the general principles which control the sculp- 

 ture of the land surfaces of the earth by rains and rivers. The volume 

 is ready for the binder. 



Geological tcorJc by Captain Button. — Captain C. E. Button resumed his 

 exploration of the same field which he has been studying for three years, 

 having recognized in it a certain unity which renders it eminently 

 adapted to an important monograph. The region explored by him is 

 centrally situated in the Territory of Utah, extending from Mount I^Tebo 

 in the Wasatch, nearly southward a distance of about 180 miles, and hav- 

 ing a maximum breadth of about GO miles. It possesses certain features 

 which serve to distinguish it both topographically and geologically, 

 and he proposes to call it the District of the High Plateaus of Utah. It 

 consists of a group of uplifts now standing at altitudes between 9,000 

 and 11,500 feet above sea-level, while the general platform of the coun- 

 try is from 5,000 to 7,000 feet high. The plateaus have been carved 

 out of this platform by great faults, and the general structure corresponds 

 closely to that described by Professor Powell under the name of the 

 Kaibab structure, and illustrated by him in his section of the region 

 traversed by the Grand Caiion of the Colorado. The relations of this 

 belt of high plateaus to the regions adjoining are of sjjecial interest. 

 At the close of the cretaceous the country lying to the eastward of it 

 passed by gradation from an oceanic to a lacustrine condition, the inter- 

 mediate stage presenting, doubtless, a strict analogy to the condition of 

 the Baltic. This eocene lake area now constitutes the southern part of 

 the drainage-system of the Colorado Eiver. During cretaceous and 

 eocene time, the area now occupied by the Great Basin was dry land, 

 and its denudation must have furnished a large part of the sediments 

 which were spread over the bottom of the great lake. The movements 

 which took place during the eocene at last resulted in the desiccation of 

 the lake, and though a strict chronological correlation to European and 

 other divisions of time cannot be made with certainty, it may be provis- 

 ionally inferred that this desiccation was completed before the commence- 

 ment of the miocene. It was brought about by the more rapid uplifting 

 of the lake area than that of the Great Basin, until at last the former 



