GEOLOGICAL CEOSS-SECTIONS. -211 



Ou Prospect Peak we liave a sharp anticlinal fold, Avith beds on both 

 sidi's of the fault standing- at an angle of 70°, but without any g-reat amount 

 of faulting-. 



In certain of the Great Basin ranges the axial plane occin-s along the 

 center of the ridge, as seen at Ravens Nest in the Pinon Range. In others 

 it follows along the edge of the uplift, an escarpment usually facing the 

 valley. Of this latter structure, Newark Mountain is an excellent example. 

 In some of these ranges there may be no faulting- of strata along, the axis of 

 the anticline ; in others it may be confined to a few huudn-d feet, or the 

 faulted block may have suffered a downthrow measured b)' thousands of 

 feet. In the latter instance it is easil}- seen that the strata along the down- 

 throw side may be lost to sight, being carried down belo\N' the present level 

 of the Pleistocene deposits. Where this is tlie case only one side of th(^ 

 fold is exposed, leaving a simple monocliual ridge. This is wliat has 

 actually occun-ed in several of the narrow uplifts in the Cli-eat Basin. 



GEOLOGICAL CROSS-SECTIONS. 



These sections, atlas sheet xiii, will be readily comprehended when 

 examined in connection with the geological map, and the detailed descrip- 

 tions of each block of Paleozoic sediments as given in the text may be fol- 

 lowed easily without much additional explanation. As the sections have 

 been consti-ucted, as far as possible, across the strike of the beds, and for 

 the most part at right angles to the principal meridional lines of faulting, 

 they measure with a considerable degree of accuracy the amount of displace- 

 ment and indicate approximately the comjjression of strata. All sections are 

 carefully drawn on a scale of 1,600 feet to the inch, with a base line taken 

 at G,000 feet above sea level, the height of the adjacent valleys on all sides. 

 So far as practicable they have been selected to show the average thickness 

 of all sedimentary rocks, from the base of the Cambrian to the summit of 

 the Carboniferous. Of course all undei'ground structure is based upon 

 observed dips and strikes taken at the surface, but these have been 

 obtained, so far as j)ossible, at frequent intervals and with every precaution 

 which could be exercised. In a countrA' so broken by faults, dislocated by 

 igneous outbui'Sts, and where bedding planes are so frequently wanting, the 



