60 APPENDIX TO KEPORT OF THE SECRETARY. 



tions of the valleys they seem to pass gradually iuto the more modern 

 deposits. 



The interesting soda-springs at the bend of Bear Eiver were carefully 

 examined. 



Although the area surveyed by the Green Eiver division was large, 

 comprising about 13,000 square miles, large collections of fossils (many 

 of them new) were made. Notes were obtained for the preparation of 

 a geological map of the area, and data collected for the elucidation of 

 many interesting problems in relation to the age of the mountains. 



Coal-outcrops were noted at a number of localities, on some of the 

 branches of the Upper Bear Eiver and of Green Eiver. The famous salt- 

 works on a branch of Salt Eiver were also examined. 



Professor St. John reports the Teton district to be one of great inter- 

 est. He found extensive areas covered with rocks of igneous origin, ba- 

 salts, and trachytes. 



The Snake Eiver plains are everywhere floored with basaltic rocks. 

 They extend up the valley of the Snake as far as the lower basin, where 

 they are succeeded by other volcanics, mainly trachytes. The latter are 

 observed inclining at greater or less angles and appear to be more an- 

 cient than the basalts. The Blackfoot Valley and the valley depressions 

 between the Blackfoot Mountains and the Caribou Eange are floored 

 with basalts in every way similar to those occurring in the Snake Eiver 

 plains. These extend southward iuto Dr. Peale's district. 



Ehyolitic products were found at a few localities. In one instance the 

 eruptive matter appears as a dike in the crest of a low, short ridge be- 

 tween the Blackfoot and Caribou Eanges, its eruption having tilted the 

 sedimentary deposits into an anticlinal ridge. 



In Caribou Mountain, also, interesting phenomena were observed. The 

 mountain is a mouoclinal ridge, made up of sedimentaries, between 

 whose strata the igneous material is intruded, appearing from a distance 

 like veritable beds of deposition, while the bulk of the west portion of 

 the mountain appears to consist of an enormous mass of erujDtive mat- 

 ter thrust up from below. This mountain would therefore appear to be 

 another instance of local outburst, similar to those brought to light by 

 the survey in Western and Southwestern Colorado. 



Extensive areas of the district are occupied by sedimentary or strati- 

 fied rocks, which were referred to the Lower Silurian, Carboniferous, 

 Jura-Triassic, Cretaceous, and Tertiary ages. These rocks have been 

 subjected to considerable folding and displacements in the different por- 

 tions of the district. 



One of the most interesting discoveries was that of the presence of 

 Qsh-remains in the Lower Carboniferous. Several forms were found, 

 identical with or closely allied to Keokuk species of the genera Cladodus, 

 Petalodus, Anthlodus, and Helodus. 



In the upper basin of Snake Eiver, Tertiary lacustrine beds occur. 

 These are probably the equivalents of the lake- beds of Dr. Hay den. 



The Teton Eange was examined and found to be a gigantic monoclinal 



