EVIDENCE OF UNCONFORMITY. 381 



son limestone, and the Mormon sandstone, completely surrounded by 

 eruptive rocks. The thickness of the Jurassic rocks in mount Jura is 

 2,000 feet. The occurrence of so large a mass of rocks, the newest of the 

 scries well exposed for so short a distance, while the associated older 

 rocks upon the sides extend beyond, tends to show that beneath the Jura 

 there is an unconformity. 



The strongest evidence, however, is found in the occurrence of a large 

 exposure of the fossiliferous Hosselkus limestone at an elevation of 4.800 

 feet, on the slope of* 1 rizzly mountain (figure 4), about two miles southwest 

 of Genesee (Hosselkus 1 ). The strike of the limestone at this point carries 

 it directly beneath the middle portion of mount Jura, where it is com- 

 pletely covered up by the unconformably overlying Jurassic rocks. 



N.E. 



/ 



' '' >;: 57T77I^#**' 



i 



'ilea. 



Figure 4.— Section on northeastern slope of Grizzly Mountain. 

 9 = p reman beds; U = Hosselkua limestone; 13 = Robinson beds; L6 = Taylorville slates; 

 18 = Grizzly quartz; E = Eruptive rocks. 



The sedimentary rocks lying immediately west of the Jurassic are the 

 hon-fossiliferous gray sandstone near Donnerwirth's, the Grizzly quartzite, 

 and the Montgomery creek limestone. At least one of these is certainly 

 Silurian, and all are Paleozoic. To the eastward the Jurassic beds are 

 bounded by the Trias. The presence of rather heavy and coarse con- 

 glomerates in the Foreman beds, as well, as delicate land plants in the 

 same series. clearly indicates that the youngest Triassic beds of the Tay- 

 lorville region were laid down not only in shallow seas bu1 near land. 



The dip of the strata, as shown in the long section i figure 1 i, from the 

 Silurian at the summit of Grizzly on the one band, across the Jurassic 

 of mount Jura into the Triassic on the other, is uniformly southwest- 

 ward. The Jurassic is thus folded in between the Paleozoic and the Trias, 



