GG APPENDIX TO THE REPORT OF THE SECRETARY. 



The moraiiial deposits are also fouud ou a grand scale in the Snake 

 Kiver Valley, ou the east side of the Teton Range. The numerous lakes 

 have been the beds of glaciers, and the shores of the lakes are walled 

 with uiorainal ridges. North of the Teton Mountains the prevailing 

 rocks are of modern volcanic origin, and in the Yellowstone Park the 

 hot springs and geysers are the later manifestations of the intense vol- 

 canic activity that once existed. All these interesting features were 

 studied with care, and the results will be elaborated for the twelfth an- 

 nual report of the survey. 



Mr. W. H. Holmes acted as geologist to the secoud division. The 

 first mouth of the season he wa^ with the fourth division, which pro- 

 ceeded from Point of Rocks Station northward, along the west side of the 

 Wind River Mountains, and up the Snake River Valley to the Yellow- 

 stone Park, where he joined the second division. In the mean time he 

 was engaged in making sketches, panoramic views, and geological sec- 

 tions of the intermediate country, all of which will i)rove of the highest 

 imi)ortance in illustrating the geological structure of this most interest- 

 ing and complicated region. 



The latter part of the summer was spent in making detailed geological 

 examinations in the district that includes the National Park. The greater 

 portion of the park was found to be covered with somewhat uniform 

 flows of the ordinary volcanic rocks. Features of more than ordinary 

 geologic interest occur, however, along the northern border of the park 

 district. Here a small belt, not more than 15 by Si) miles in extent, con- 

 tains a fair epitome of the geology of the Rocky Mountain region. The 

 whole series of formations from the earliest to the most recent are almost 

 typically develoi^ed. The only marked irregularity in the succession of 

 geologic events occurred during the great mountain-building period of 

 the early Tertiary. After that followed a number of inferior oscillations 

 of the surface, during which an extensive series of recent Tertiary and 

 volcanic rocks were deposited. Connecting this ])eriod with the present 

 are the deposits of a number of great lakes, which at the present time 

 have their chief representative in Yellowstone Lake. 



The formations of the Tertiary period present features of more than 

 ordinary interest. They consist of upward of 5,000 feet of strata which 

 .are almost totally made up of fragmentary volcanic products. The whole 

 period seems to have been one of unparalleled volcanic activity, the lat- 

 ter i)art esi^ecially having yielded such immense quantities of ejecta that 

 the strata are almost wholly breccias and conglomerates. These forma- 

 tions are therefore so unlike those of corresi)ondingperiods in neighboring 

 provinces that it is almost impossible, considering the absence of both 

 vertebrate and invertebrate remains, to make satisf\ictory correlations. 

 This difiiculty is increased by the fact that these formations have a much 

 .greater elevation than those of any of the neighboring basins of the 

 interior or eastern i)lains districts. They lie in a horizontal position, 

 upon the eroded surfaces of the strata of precediug ages, at an eleva- 

 tion of from 0,000 to 11,500 feet above the sea. 



