i'j;c)81m:ct iiid(je. 19 



gives out find the fault enters the Xevadu liuiestoue with :i course a little 

 east of north, and follows alonj^- under the a]jru])t east wall of Sui;ar I^oaf. 

 A short distanee beyond Suyar Loaf tlie fault coincides with tlic contact of 

 the Nevada limestone with the White Pine shale, niaintainiu;;- this course 

 until both the liuiestoue and shale pass Ijeneath the basalt tableland toward 

 the north. That the fault continues bevond this point beneath tlie l)asalt 

 is clearly established by geological structure, the Devonian sti-ata of (Jouuty 

 Peak jjassiug luider the tableland on the west side and the Weber con- 

 glomerate and Upper Coal-measures dipping towai'd it and passing l)eneath 

 it on the east. There can be no doubt that the Kescue fault sharply defines 

 a great physical break separating the County Peak from the Diamond Peak 

 block. After entering the region occupied by the basalt field, there is no 

 means of determining the precise course of the fault, everything Ijeing 

 obscured by recent lavas. Upon leaving the basalt area the fault probablv 

 follows along the east base of Richmond Mountain, but is hidden beneath 

 the audesitic rocks that, flowing eastward, rested against the base of the 

 gently iuclined slopes of the Upper Coal-measure limestones of the Dia- 

 mond Range. Beneath the lavas the trend of the fault, while in a great 

 degree conjectural, cannot \ary far from the course of the contact between 

 the Nevada limest(meand the White Pine shale as exposed to the soi.th and 

 the Une of the ('arl)oniferons rocks to the north and east. In the region of 

 the volcanic rocks the displacement along the fault can not be measm-ed, 

 although it must be very great, as is shown by the Devonian beds on the 

 one side and the uj)per members of the great development of the Carbon- 

 iferous sediments on the other South of the basalt the fault runs wholly 

 within the limits of the upper portion of the Nevada limestone, or else at 

 the base of the White Pine shales. Nowhere along its entire course, from 

 Packer Basin to Fish Creek Valley, does the downthrow apparently exceed 

 3,000 feet of vertical displacement. 



OROGR.\PIIIC I5LOCKS. 



Prospect Ridge.-Tliis ridge stauds out as the most jn'ominent orographic 

 feature of the iMn-eka Mountains. It is situated in the very center of the 

 mountains and presents a bold, serrated outline, extending with an appmx- 



