PEALE.J RESUME CENOZOIC ROCKS— TERTIARY. 



The following is tlie section of tlie Tertiary formations : 



Tertiary section. 



635 



In tMs section I have included only the undoubted Tertiary. At no 

 place was the Salt Lake Group seen resting on the Bridger Group, nor 

 was the latter well shown anywhere in the district. 



WAHSATCH GROUP. 



After the Post-Cretaceous uplift the region of the Green Eiver Basin 

 was occupied by a lake which extended westward in our district to the 

 Bear Eiver Eange. It ajjpears that in its early stages this lake was 

 much smaller than the area , now covered «by the deposits indicates, for 

 wherever the beds referable to the period were seen, they were found 

 resting on the upturned and much eroded edges of the older strata, which 

 include rocks from Silurian age to the Laramie Grouj), and the deposits 

 rei^resent only the upper part of the group. 



The largest areas of the Wahsatch are in the northern portion of the 

 Green Eiver Basin, where a large part of the surface is covered by its 

 deposits. The overlying Green Eiver Group in this region is mostly 

 absent, having been eroded away. Isolated buttes, however, still remain, 

 ]iroving its former existence and extension over the whole region. Along 

 the southwestern slopes of tlie Wind Eiver Mountains the Wahsatcli 

 beds rest on the granitic rocks, and were evidently derived from the dis- 

 integration of the granitic rocks that farther to the eastward make up 

 the main range. They consist of yellow, gray, and pink sands and marls, 

 which dip from 5° to 10° from the mountains. West of Green Eiver the 

 character of the beds is similar to those on the east. They are generally 

 brick-red in color and weather into picturesque bad-land forms. Along 

 the edge of the basin they are found to be composed mainly of cougiom- 



