12*2 Zteyh'/'—Sitiecoux Oolites of Central Pennsylvania. 

 Fig. 7. Fig. 8. 



Fig. 7. Oolitic chert from Spring Creek. Crossed nicols. x 40. 

 Fig. 8. Oolitic chert with inclosed fragment of older siliceous oolite layer 

 at right. Crossed nicols. x 29. 



limestone, and seems to be the result of lime secretion 

 about algse. The oolites themselves are small, few attaining a 

 millimeter in diameter. They are usually enlarged by the 

 addition of radiating fibrous calcite, often deposited in several 

 concentric layers. In some of the more perfect spherules the 

 dark interference cross is faintly visible. 



Fig. 9. 



Fig. 10. 



Fig. 9. Gray oolitic limestone showing several included quartz oolites. 

 Spring Creek. Crossed nicols. x 29. 



Fig. 10. Calcareous oolite near Spring Creek, showing almost complete 

 destruction of oolitic structure due to recrystallization. Spring Creek. 

 Crossed nicols. x 29. 



