120 Ziegler — Siliceous Oolites of Central Pennsylvania. 



SiO -. 90- id', 



Fe,0,.-- -11 



A1 9 3 -\1 



CaO -3!) 



H„0 -25 



100-02$ 



The color is a beautiful light gray, and the grains are well 

 rounded, as a rule spherical ; under the microscope they show 

 usually a quartz nucleus surrounded by layers of a very fine 

 mosaic of chert. The individual spherules are nearly uniform 

 in size and are cemented by fibrous chalcedony often laid d^wn 

 in parallel layers. The layers making up the oolite and the 

 cement are alternating black and white. The relative propor- 

 tion of black and white layers present give the color to the 



Fia. 6. 



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Fig. 6. Section of oolite near Krumrine. 1 and 3, dense, siliceous lime- 

 stone ; 2, pure white quartz sandstone ; 4, calcareous oolite ; 5, siliceous 

 oolite. 



oolite ; dark oolite with white grains being due to the greater 

 abundance or thickness of the black layers ; white oolites with 

 predominant black grains, in turn, resulting from the excess of 

 light-colored layers in the oolite and the cement. 



Type Three. — Occurring about one mile north of Krumrine. 

 In a cut along the track of the Belle Fonte Central R.R., a 

 small exposure of oolite gives the following section illustrated 

 by figure 6. 



