EEGION BETWEEN BEAR AND WEB"ER RIVERS. 333 



taceous, including the Dakota conglomerates which are seen on the north slope 

 of the Upper Weber Caiion, and the mixed beds of sandstone and shales of 

 the Colorado group. Passing eastward these are both overlaid by the nearly- 

 horizontal Tertiary conglomerates, which occupy the whole top of the ridge, 

 forming the north wall of the Upper Weber Canon. This great field of con- 

 glomerates extends down to within a couple of miles of Coalville, occupying 

 the heights to the south of Chalk Creek and extending eastward all the way 

 t^ Bear River. Chalk Creek itself, almost to its head, occupies a broad 

 basin eroded out of the Tertiaries, in which are exposed the underlying Creta- 

 ceous. So also in Grass Creek, which runs parallel to Chalk Creek, a region 

 of Cretaceous is laid bare, which is connected with that developed in Chalk 

 Creek. There is here then a broad area of Cretaceous, which is bounded 

 to the north by the Tertiary conglomerate ridge running parallel with the 

 railroad on the south side of Echo Cafion, for about 10 miles from its mouth. 

 At this point, the Cretaceous swings northward across the railroad, and occu- 

 pies the lower 400 feet of the hills on the north side of the canon. It is here 

 seen to underlie the Tertiary with a clear unconformity, the inclined beds 

 dipping about 30° to 35° to the northwest, while the overlying Tertiary has 

 an inclination of not more than 5° to 8°. Passing eastward, the Tertiary 

 gradually encroaches on the Cretaceous again, and crosses the railroad 

 about 2 miles below Castle Rock Station, occupying, with the exception of 

 a few isolated outcrops like the "Needles" on Yellow Creek, the whole 

 region from this point to Bear River. 



The high tables and peaks of conglomerate which overlie the Cretaceous 

 southeast of Coalville entirely obscure its structure. It is evident, however, 

 in coming down the canon from Kamas Prairie, that in the Colorado gi'oup 

 there is a limited fold in which the rocks change their dip from a -northerly 

 to a southerly inclination, passing through a synclinal fold, and again dip- 

 ping to the north and west. So that from Kamas Prairie to Coalville, with 

 the slight exception of about 3 miles of southerly-dipping strata, the whole 

 series dip north and west. With the exception of 300 or 400 feet, which 

 may be reckoned in the Dakota group, at the base of the series, the whole 

 formation from near Peoria to just below Coalville is embraced within the 

 Colorado group. Where it directly overlies the Dakota beds, below Peoria, 



