518 DESCRIPTIVE GEOLOGY. 



a fault of between 200 and 300 feet, and a considerable compression of 

 strata, the beds occurring along the inside of the curved ridge, where they 

 are found as a synclinal fold. By reference to the upper section at the 

 foot of the geological sheet, this synclinal structure is shown, with the 

 Weber Quartzite underlying the limestone. 



Interstratified in the limestone near the summit of the ridge occurs a 

 dark-brown cherty band. From this stratum, as well as both from the over- 

 lying and underlying limestone, large numbers of organic remains may be 

 obtained, but without any great variety of species. 



From the cherty band, the following Brachiopoda have been recognized: 



Froductus Bogersi. 

 Spiriferina pulchra. 



from the limestone, in addition to the above species: 



Produdus Nebrascensis. 

 StreptorJiynchus crassus. 



Among Bryozoa, occurs an undetermined species of the genus Cascinium. 



North of Ives' Pass, the hills rise in rounded masses, stretching to the 

 northward for 15 miles, before again disappearing beneath the Quaternary 

 deposits. The strata indicate considerable folding and crumpling, and the 

 structure is much obscured. Just north of Ives' Pass, the prevailing dip 

 would seem to be to the eastward, while in the northern end it seems to be^ 

 in the opposite direction. South of Montello Creek, along the foot-hills, 

 the beds dip 3° east. The beds, so far as examined, are mainly limestones 

 and calcareous shales, and have been referred to the Upper Coal-Measure 

 series. No fossils were found in them. In these limestones are frequently 

 seen beds and irregular bodies of bluish-black cherty matter, traversed by 

 thin white seams of silica; the rock breaking with a rough, jagged frac- 

 ture. Very similar rock appears to characterize the limestone in many 

 localities, but its exact geological horizon was not clearly made out. 



On the western wall of the Desert Gap, at the extreme northern end of 

 the map, is a development of a remarkably interesting rhyolite, of a deli- 

 cate purplish-gray color, which, on the larger surfaces of fresh fracture, 

 has a wavy, lace-like structure. It is full of druse-like cavities lined with 



