COMBS PEAK. 135 



Mountain and the Nevada limest(Mics in juxtaposition witli the Prospect 

 Mountain quartzite, recent accuniubition.s, however, obscurin<> the precise 

 Hne of the displacement. The water-shed Hes nearly opposite Prospect 

 Peak. Southward from this dividing rid<i-e the valley becomes a more im- 

 portant physical featm-e, in places opening- out to more than a mile in width, 

 finalh' draining- into Antelope Valley soutlnvest of the mountains. The 

 southern end of the vallev is arid and covered with sage-l)riish, closely 

 resembling the liroader longitudinal valleys of the Great Basin. 



Mahoganv Hills occupy by far the largest area of anv moinit:iin l)lock 

 in the Eureka District, measuring 12 miles in length Ity S miles in width. 

 Nevada limestones constitute by far the greater i)art of this orographic 

 block, four epochs of the geological section — Ein-eka (juai-tzite, Lone 

 Mountain limestone, Nevada limestone, and Diamond Peak (piartzite — are 

 all rej)resented and their structural relations well shown. In presenting 

 some of the more important details of the region, it will be well to lieginat 

 the southern end, where l)oth in geological and topographical sti-ucture 

 Mahoganv Hills are closelv connected with the Fish Creek Mountains 

 through Wood Cone and the granite-porphvrv region. 



Combs Peak. On the uortli side of Wood Cone, resting uncomformably 

 upon the Eureka (piartzite, lies a body of bluish black and dark grav lime- 

 stones dipping l)eneatli the limestones of Condjs Peak. These dark lime- 

 stones everywhere form the southern slopes of the Peak, and westward of 

 the quartzite rest directly upon the granite-poi-phyry bod-v'. The hillsides 

 are sc<jred l)y frequent ravines and water-courses showing the inclination of 

 the strata northward into the mountain, ])ut lines of .stratification are 

 exceetUngly i-are, nowhere allbrding, for any ct)nsiderable distance, con- 

 tinuous dips and strikes. The best locality for observing these beds was 

 found just north of Wood Cone, on the end of the long s])ur coming 

 down from Combs Peak. Fx'om their dai'k steel-grav color and their 

 uniforndy fine grained appearance, it is easy to see that the}' differ essen- 

 tiall}' from the characteristic Lone Mountain beds observed elsewhere. This 

 is all the more noticeable, as they are found to pass into beds possessing 

 the pecvdiar habit of the latter horizon. This stnking contrast in the lime- 

 stones led to a diligent search for [)aleontological evidence of their geologi- 



