THICKNESS OF POGONIP LIMESTONE. 49 



Chemistry shows no characteristic difference between this limestone and 

 the older masses, the beds being more or less magnesian throughout their 

 entire vertical range. A complete analysis was made of a siliceous variety, 

 taken from near Wood Cone, yielding the following result : 



Silica 9-345 



Alumina 0-309 



Ferric oxide 0-289 



Ferrous oxide 



Manganese 



Lime 50-011 



Magnesia : 0-535 



Water 0-130 



Carbonic acid 39-111 



Phosphoric acid 0-240 



Chlorine 0-030 



Organic matter Traces. 



Alkalies Traces. 



Total 100-000 



To the east of Jackson Mine, where the beds are well exposed and lie 

 inclined at a nearly uniform angle, they measure 2,700 feet across their 

 greatest development. This thickness is probably surpassed by the beds 

 on the long spur southwest of Wood Cone, but there they stand nearly ver- 

 tical, in some places dipping eastward and in others westward, occasionally 

 showing evidences of faulting, which prevents any reliable estimate of their 

 thickness. It is probable they measure over 3,000 feet. An estimate of the 

 strata at White Pine gives over 5,000 feet of limestone. At first sight it would 

 appear as if there must have been some displacement of beds along Pros- 

 pect Mountain, but the succession of a rich fauna with the same character- 

 istic specific forms at the base and summit of the epoch at both Eureka and 

 White Pine would preclude such a supposition and the simplicity and uni- 

 formity of structure go to show that such is not the case. 



Fauna of the Pogonip Epoch. Throughout the entire thickness of the Pogo- 

 nip beds, organic remains characterize the epoch. At the base there is a 

 decided mingling of species, a number of Potsdam forms extending up- 

 ward for some distance into the limestone. Passing upward, however, 

 these species gradually diminish and there comes in rapidly a numerous 

 fauna representing higher and higher forms, till midway in the beds nearly 

 MON xx 4 



