CHAPTER IV. 

 DEVONIAN AND CARBONIFEROUS ROCKS. 



DEVONIAN ROCKS. 



By imperceptible gradations limestones of the Lone Mountain epoch 

 pass upward into those of the Devonian period, and as no definite horizon 

 separating them has as yet been determined 110 accurate measurements of 

 their respective thicknesses can be given. Devonian rocks cover a far 

 greater area in the district than those of any other period; they are much 

 more widely distributed and present a thickness greater than either the 

 Cambrian or Silurian. In no part of the Great Basin are they better 

 exposed than at Eureka, and as nowhere else have they been so carefully 

 investigated the district must long remain a typical one for the study of 

 Devonian strata. Notwithstanding the beds present a rich fauna, only two 

 subdivisions of the Devonian have been made first, Nevada limestone, and 

 second, White Pine shale although taken together they have a thickness 

 of about 8,000 feet, This division is based upon a marked change in both 

 the fauna and character of the sedimentation. 



Nevada limestone. The name selected to designate this horizon is taken 

 from the name of the state where the epoch is so well represented by a 

 broad development of beds and the only state or territory in the Great 

 Basin where it has been recognized as attaining any great thickness and its 

 limits and geological relations studied. As the designation of the epoch 

 would suggest, the beds throughout the entire series are composed mainly 

 of limestone, although intercalated beds of shale, quartzite, and sandstone 

 occur. The Lone Mountain and Nevada limestones taken together present 

 an immense thickness of beds, lying between the Eureka quartzite and 

 White Pine shale. Together they measure about 7,800 feet in their broad- 

 est development. The division into Silurian and Devonian is based mainly 

 upon paleontological grounds. The transition in sedimentation from char- 

 acteristic Silurian to unmistakable Devonian is so imperceptible that a 



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