APPENDIX TO REPORT OF THE SECRETARY, 59 



sedimentary formations were noted. In the region between tbe Seminoe 

 Hills and Eawlins, on the Union Pacific Eailroad, an interesting group 

 of mud-springs, analogous to the mud-puffs of the Geyser region, were 

 seen. About four hundred of these curious springs were found and ex- 

 amined. 



After finishing his work with the field-party, Dr. Endlich visited the 

 coal-mines near Evanstou, Wyo., to examine the coal-bearing rocks of 

 that region. 



The Green Eiver district lies directly west of the Sweetwater district. 

 With the exception of a small area of granite, along the southwestern 

 side of the Wind Eiver Mountains, and some basaltic flows in the north- 

 western portion of the district, the rocks are sedimentary. The Green 

 Eiver Basin was the first area surveyed. The prevailing formation was 

 found to be the Green Eiver group of the Tertiary, underlaid by the 

 Wahsatch. Toward the south, buttes of the Bridger clays rest on the 

 Green Eiver marls and sandstones. They are the northern outliers of 

 the extensive Bridger areas found farther southward. 



On the northeast, the Tertiary beds rest on the granites of the Wind 

 Eiver Mountains, the line of junction being considerably obscured by 

 morainal material. One of the most interesting points noted in the 

 Green Eiver Basin was on its west side, where the Wahsatch Tertiary 

 is seen resting uncouformably on Jurassic and Cretaceous strata. At 

 one point. Carboniferous fossils were obtained from bowlders of lime- 

 stone found in a conglomerate in the Wahsatch group. These were 

 derived without doubt from the Carboniferous limestones of the mount- 

 ains that stand a short distance to the westward, and which must once 

 have formed a portion of the shore-line of the lake filling the Green 

 Eiver Basin. 



An arm of this Tertiary lake extended up Harris Fork of the Green 

 Eiver, where Green Eiver and Wahsatch beds are found in horizontal 

 position. In the Green Eiver shales, at several localities, good collec- 

 tions of fossil fish and insects were found, among which were many new 

 species. 



The region of the Blackfoot Eiver, in the northwestern part of the 

 district, is covered in all its lowest portions with flows of basalt which 

 had their origin in craters that still show between the Blackfoot, Bear, 

 and Portueuf Eivers. The pouring out of this basalt must have occurred 

 either during or just prior to the present period, as there has been but 

 little if any change in the surface since the eruption. On the Portneuf 

 Eiver a narrow tongue of basalt extends almost to Snake Eiver Valley. 

 The surface of this basalt slopes somewhat, but not so much as the pres- 

 ent bed of the Portneuf. The lower valley of the Portneuf is interesting 

 from the fact that it is probably one of the ancient outlets of the great 

 lake that once filled the Salt Lake Basin and extended across into 

 Cache Valley. In Cache Valley and Malade Valley, modern Tertiary 

 deposits are found jutting against the mountains, and in the central por- 



