Reviews — F. V. Haydens XT. 8. Geological Survey Reports. 227 



border, grazing land exists only in small patches of a few acres each. 

 There are not, so far as is known, any mines or mineral deposits 

 within the 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 30 miles in extent, contains a fair epitome of 

 the geology of the Eocky Mountain region. The whole series of 

 formations from the earliest to the most recent are almost typically 

 developed. The only marked irregularity in the succession of geo- 

 logic events occurred during the great mountain-building period of 

 the Middle 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 

 period with the present are the deposits of a number of great lakes, 

 which at the present time have their chief representatives in the 

 Yellowstone Lake. 



The third party surveyed the Wind Eiver Mountains, the 

 Wyoming and G-ros Ventres ranges, and a large area of the Snake 

 Eiver Valley. 



Dr. Hayden accompanied the fourth or photographic division, and 

 the route pursued gave him an opportunity to secure a very accurate 

 general knowledge of the geological structure of a large area. The 

 Wind Eiver Eange proved one of remarkable interest. It has a 

 trend about north-west and south-east, with a length of about 100 

 miles. On the west side all the sedimentary belts have been swept 

 away, down to the Archaean, older than the Wahsatch, and the latter 

 formation rests on the Archaean rocks all along the base of the range, 

 seldom inclining more than 5° to 10°. On the east side of the range 

 the seams of sedimentary formations usually known to occur in the 

 north-west are exposed from the Potsdam Sandstone, which rests 

 upon the Archaean rocks, to the Cretaceous inclusive. 



Along the north-western portion of the range the Wahsatch 

 Group only is seen for some distance,, but as we proceed down the 

 Wind Eiver Valley the formations appear one after the other, until at 

 the lower end the entire series is exposed. The Wind Eiver Eange 

 may be regarded as originally a vast anticlinal, of which one side 

 has been entirely denuded of its sedimentary series, except the Middle 

 Tertiary. On the same side of the range the morainal deposits and 

 glaciated rocks are shown on a scale such as we have not known 

 in any other portion of the West. Three genuine glaciers were 

 discovered on the east base of Wind Eiver and Fremont Peaks, the 

 first known to exist east of the Pacific coast. 



The morainal deposits are also found on a grand scale in the 

 Snake Eiver Valley, on the east side of the Teton Eange. The 

 numerous lakes have been the beds of glaciers, and the shores of the 

 lakes are walled with morainal ridges. North of the Teton Moun- 

 tains the prevailing rocks are of modern volcanic origin, and in the 

 Yellowstone Park the hot springs and geysers are the later manifes- 

 tations of the intense volcanic activity that once existed. 



