64 <;EOLOGY OF THE EUKEKA DISTRICT. 



boundary between them is impossible to establish, and, as is usually the 

 case where beds form a continuous, conformable limestone series, a line 

 of separation based upon faunal changes must always remain more or less 

 arbitrary. Lithologically, in their broader features, the Silurian and 

 Devonian limestones are quite distinct; it is only in the intermediate beds 

 that no line can be drawn. The light gray and white siliceous beds that 

 form the mass of the Lone Mountain present a wide vertical range, and 

 in these beds are occasionally seen obscure impressions of Niagara corals, 

 and in other localities, in similar rocks not much higher up in the series, 

 occur Atrypa reticularis and other forms foreshadowing the Devonian. It 

 is known that characteristic Lone Mountain beds carrying Hah/sites 

 catenulatus extend for nearly 1,500 feet above the Eureka quartzite, and 

 that beds easily identified by their organic remains bring the Devonian 

 down to about 6,000 feet below the summit of the great limestone belt 

 lying between the Eureka quai-tzite and White Pine shale. Hatysites and 

 Atrypa reticularis were never found associated together, although it can not 

 be definitely stated that the former fossil does not appear as low down in 

 the limestone as the highest occurrences of the characteristic coral. 



The Nevada limestone presents broad elevated rock-masses character- 

 ized by bold escarpments and castellated summits. Profound orographic 

 movements have broken this great body of limestone into massive blocks 

 intersected by gorges and canyons, affording a mountain scenery both 

 grand and picturesque, and one rarely equaled in any limestone region of 

 the Great Basin. Although these uplifted blocks afford abundant geological 

 exposures across the greater part of the limestone, in no one instance is 

 there a complete or in every way satisfactory section from base to summit. 

 In many localities the exposures extend upward from the summit of the 

 Lone Mountain several thousand feet into the Nevada beds; in others the 

 strata are well shown from the top down till cut off by some line of faulting 

 which hides all the lower limestones. Frequently the lower beds of the 

 Devonian are buried beneath the Quaternary plain. The region, how- 

 ever, affords many excellent and overlapping sections exposing from 4,000 

 to 5,000 feet of rock; one continuous series of beds being estimated at 5,400 

 feet, which includes nearly the entire Nevada epoch. Throughout the 



