7^ T. C. BROWN OOLITES AND OOLITIC TEXTURE 



Plate 28.' — Micro-sections of ooliUc Structures 



Figures 1 to 5. — Siliceous oolites from State College, Pennsylvania. 



All figures except 5 X "20. Figure 1 is with plain light and shows 

 the bands of iron oxide. In figure 2 one of the oolites has two 

 sand grains in its center ; nicols crossed. Figure 3 shows four 

 types of sections from these oolites. In one there is a sand 

 grain secondarily enlarged and showing a quartz crystal out- 

 line and a zone of minute rhombic crystals within tliis enlarge- 

 ment. Another oolite has a plain sand grain at the center, a 

 third a granular center, and a fourth a fibrous center (see text- 

 figure 1). Nicols crossed. Figure 4 shows three oolites with 

 enlarged sand-grain nuclei; nicols crossed. Figure 5 is the 

 center of the granular oolite grain of figure 3. X 100. 



FiGtTRE 6. — Siliceous oolite from Bitter Creek, Wyoming. 



Showing f oraminif eral skeletons in the interspaces. X 20. 



