COMBS PEAK. 135 



Mountain and the Nevada limestones in juxtaposition with the Prospect 

 Mountain quartzite, recent accumulations, however, obscuring the precise 

 line of the displacement. The water-shed lies nearly opposite Prospect 

 Peak. Southward from this dividing ridge the valley becomes a more im- 

 portant physical feature, in places opening out to more than a mile in width, 

 finally draining into Antelope Valley southwest of the mountains. The 

 southem end of the valley is arid and covered with sage-brush, closely 

 resembling the broader longitudinal valleys of the Great Basin. 



Mahogany Hills occupy by far the largest area of any mountain block 

 in the Eureka District, measuring 12 miles in length by 8 miles in width. 

 Nevada limestones constitute by far the greater part of this orographic 

 block, four epochs of the geological section Eureka quartzite, Lone 

 Mountain limestone, Nevada limestone, and Diamond Peak quartzite are 

 all represented and their structural relations well shown. In presenting 

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

 the southern end, where both in geological and topographical structure 

 Mahogany Hills are closely connected with the Fish Creek Mountains 

 through Wood Cone and the granite-porphyry region. 



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

 upon the Eureka quartzite, lies a body of bluish black and dark gray lime- 

 stones dipping beneath the limestones of Combs Peak. These dark lime- 

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

 the quartzite rest directly upon the granite-porphyry body. The hillsides 

 are scored by frequent ravines and water-courses showing the inclination of 

 the strata northward into the mountain, but lines of stratification are 

 exceedingly rare, nowhere affording, for any considerable 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 spur coming 

 down from Combs Peak. From their dark steel-gray color and their 

 uniformly fine grained appearance, it is easy to see that they differ essen- 

 tially from the characteristic Lone Mountain beds observed elsewhere. This 

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

 the peculiar habit of the latter horizon. This striking contrast in the lime- 

 stones led to a diligent search for paleontological evidence of their geologi- 



