EPOCDS SEPARATING THE GROUPS. 69 



the lower beds, as it does in places, where they are also found to be more 

 indurated and more or less massive sandstones. The conglomerate which 

 is found in the middle of the group is persistent over a very large area, and 

 the whole group is characterized throughout the entire province by the 

 occurrence of silicified wood in large quantities Sometimes trunks of trees 

 from fifty to one hundred feet in length are found. The Shinarump Con- 

 glomerate is usually very hard, and weathers in such a manner as to form 

 hog-backs or cliffs, and the softer gypsiferous beds above, when carried 

 away by rains, leave behind fragments of this silicified wood, so that the 

 Shinarump Conglomerate is often covered with great quantities of this ma- 

 terial. Shinarump means literally "Shin-au-av's Rock." Shin-au-av is one 

 of the gods of the Indians of this country, and they believe these tree- 

 trunks to have been his arrows. 



The plane of demarkation between the Shinarump Group and the sum- 

 mit of the Carboniferous is always well marked. Soft, gypsiferous shales are 

 found at the base of the upper group, and cither a pure limestone, a cherty 

 limestone, or a homogeneous sandstone, at the summit of the Carboniferous. 

 In places, however, a conglomerate is found at the base of the Shinarump 

 Group, its coarser fragments being composed of cherty limestone which con- 

 tains Upper Carboniferous fossils. So in some places, at least the epoch of 

 change was a period of erosion. Flaming Gorge Group contains Jurassic 

 fossils from* its summit to its base, but the fossils found in the next three 

 groups below are few and very imperfect; hence we cannof correlate these 

 groups with the general geological succession which has been established 

 throughout the world, but we know they lie between the Jura above and the 

 Carboniferous below. 



THE CARBONIFEROUS GROUPS. 



The grouping* of the Carboniferous beds is fully set forth in the section 

 on page , r >7. The base of the Carboniferous series is not found in Cataract 

 Canon, but in the Uinta Mountains these beds rest unconformably upon 

 the Uinta Group. In the Grand Canon, they rest unconformably upon 

 the Grand Caiion Group and also upon the crystalline schists; hence in 

 both places the plane of demarkation is important, and represents long 

 periods of erosion. 



