CHAPTER IV. 

 DEVONIAN AND CARBONIFEROUS ROCKS. 



DEVONIAN ROCKS. 



By imperceptible g-radations limestones of the Lone Monntain ei)och 

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

 separatinji' them has as yet been determined no accurate nu'asui-ements of 

 their respective thicknesses can be g-iveu. 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 thev been so carefully 

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

 Devonian strata. Notwithstanding the beds present a rich taun;i, onK- two 

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

 second, White Pine shale — although taken together thev have a thickness 

 of about <s, ()()() feet. This division is l)asedupon 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 tlie epoch is so well represented by a 

 broad development of ])eds 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 

 woidd suggest, the lieds 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 (piartzite and 

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

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

 upon paleontological grounds. The transition in sedimentation from char- 

 acteristic Silurian to unmistakable Devonian is so imperceptible that a 



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