386 J. S. DILLER GEOLOGY OF THE TAYLOHVILLE REGION. 



A rather coarse gray sandstone, with a gentle southwesterly dip, is 

 found lying unconformably upon more highly inclined red calcareous 

 beds, which contain a number of small lenticular masses of gray lime- 

 stone. No fossils were found in this locality in the red beds, but they 

 are between the porphyrite and the Mormon sandstone, which is full of 

 fossils: and the red beds themselves on the next spur to the southward 

 contain Opis and an abundance of the screw-shaped gasteropods which 

 characterize the Thompson limestone. In the overlying sandstone an 

 ammonite was found, and from the lithologic character of the rock it is 

 believed to belong to the upper portion of the Hardgrave sandstone. 

 Whatever its geologic horizon, its present position is due to displacement 

 from the southwestward, where the Hardgrave sandstone is exposed. 



On the prominent spur which reaches the stage road in the bend by 

 the narrows, one-third of a mile south of Donnerwirth's, at an elevation 

 of 4,550 feet, a small mass of Hardgrave sandstone, with its characteristic 

 fossils, occurs directly upon the Mormon sandstone, equally well defined 

 by its fossils. The conglomerate near by is the one belonging to the 

 middle portion of the Mormon sandstone. Figure 8 is a section of the 

 exposure, and it is evident that the Hardgrave sandstone has beenshoved 

 into its present position from a short distance southwestward, where it 

 is well displayed near the base of the mountain. 



At a number of points on the western slope of mount Jura, a little 

 above the elevation of 4,o00 feet, small masses of Hardgrave sandstone 

 occur, but as they are enveloped by porphyrite it is not so apparent that 

 they have been faulted into their present position. A short distance 

 further up the slope there is evidence of the faulting found in the breccia 

 which underlies the siliceous eruptive. The breccia occurs at a number 

 of points along the course of the fault. It is composed largely of the 

 fragments of the superior rock and may he an eruptive, hut a more 

 plausible explanation attributes its origin to faulting. 



The two outcrops noted in figures 7 and 8 are in the line of the general 

 displacement, which causes a repetition of the oldest three Jurassic for- 

 mations in mount Jura, and it is desirable to note that the amount of 

 displacement in the two cases is different. While in the first case the 

 Hardgrave sandstone is carried over upon the Thompson limestone, in 

 the second it is carried beyond the Thompson limestone to near the mid- 

 dle of the Mormon sandstone, indicating that the amount of displacement 

 in mount Jura is greatest in its southern portion. The same feature is 

 more forcibly illustrated by the relation of the two masses, each of which 

 is made up of the three repeated formations in mount Jura. While on 

 the southern slope of the mountain these are separated by a throw of at 

 least three-fourths of a mile, on the northern portion the displacement 



