WEBER CANOK 391 



which the outcrops occur are irregularly eroded and much covered with 

 earth. Thence to the top of the series, where they pass under the Tertiary 

 conglomerates of the "Narrows", the Jurassic series is entirely made up of 

 alternating calcareous and argillaceous shales and sand-beds. Their aver- 

 age dip is 78° to the eastward, and the prevailing bedding very thin and 

 shaly. At various points, notably near the top of the series, there are 

 extremely well-developed ripple-marks. The strike is about 16° to 18° east 

 of north. The whole thickness cannot be less than 1,500 feet, and may 

 possibly reach 1,800. Upon the hills to the south of the river, two bold 

 blade-like outcrops of the edges of strata stand out conspicuously, and are 

 known as the ''Devil's Slide". The soft, intermediate, shaly strata have 

 been worn down, leaving a steep, narrow passage-way between two high 

 walls. From Morgan Valley up to the uppermost members of the Jurassic, 

 we have about 18,000 feet of conformable rocks, and here the conformable 

 series ends. There may be some few higher members of the Jurassic which 

 are lost under the overlying non-conformable Tertiary conglomerates of the 

 Narrows, but they cannot be either tliick or important, as the whole series 

 seems to be represented here which was found on the Upper Weber at Peoria, 

 where it is overlaid by the conformable Cretaceous. 



A short distance up the valley of Lost Creek, to the north of the vil- 

 lage of Croydon, an obscure conglomerate is seen overlying the Jurassic beds 

 unconformably, the latter holding their regular dip of 78°, and the former 

 dipping only 25° east, with a discrepancy also in the strike, the Jurassic 

 striking about 16° east of north, while the conglomerates trend 26° to 28° 

 east of north. Directly southeast of this, and across Lost Creek, there is an 

 outcrop, lying parallel to the stream, and therefore conformable with the 

 conglomerate above mentioned, which has also a dip of about 25° to the 

 southeast, and contains numerous Cretaceous fossils. This outcrop is partly 

 of fine conglomerate, but chiefly of buff and cream-colored gritty sandstones. 

 These are overlaid by black shales, which, with the sandstones, undoubtedly 

 belong to the Colorado group. From their position underneath the Colorado 

 beds, and unconformity with the Jurassic, it was concluded that these 

 fragments of conglomerates represent all that is left in this locality of the 

 Dakota Cretaceous. A half a mile up the valley, both the conglomerates 



