/8 PROCEEDINGS OF THE TRINCETON MEETING 



not concentrically arranged. It consists of an earthy mass, sometimes slightly 

 stained with iron oxide, with extremely small crystals of what seems to be 

 barite arranged along open spaces and mixed with the earthy material. It is 

 r)ossible that some of these crystals are barium-orthoclase, as the optical prop- 

 erties would correspond to those of that mineral. The interference colors are 

 bluish gray and the extinction angle is zero or very small. A little calcite 

 was found in two thin-sections and a little quartz in another, while it is believed 

 that a small amount of clay is also present. In four thin-sections examined 

 and in the large number of concretions crushed for puriwses of analysis no 

 definite body, such as a sand grain or similar structure, was found serving as 

 a nucleus. Outside of the earthy, central mass the material is concentrically 



F^.2 



F,:g.4 



%.5 



F^.2 



Flg.G 



Figure 1. — Thin-sections of oolitic and pisolitic Barite 



Figures 1 and 2. Pisolitic barite (3 diameters). Figure 3. Barite ring resembling 

 travertine (3 diameters). Figure 4. Large oolites (2 diameters). Figure 5. Thin-sec- 

 tion of oolite, showing central structure and fine lines (25 diameters). Figure 6. Thin- 

 section of oolite without well marked concentric spheres. 



arranged and the spheres marked by very fine lines. It appears that the con- 

 cretions began to form by deposition of barite in both a crystalline and earthy 

 condition, with small amounts of other minerals, and that this later continued 

 to precipitate more rapidly in a purer condition, either as a replacement of 

 some other mineral or in open spaces in the sand. No evidence of replacement 

 is found unless it be the traces of calcite existing in some oolites, as the con- 

 cretions are loose and not embedded in a solid rock. 



In color the oolites are white to bluish gray, and they are very smooth on 

 the outer surface. From their appearance they were at first thought to be 

 chert concretions, but an examination showed a specific gravity of 4.25 and a 

 flame coloration for barium, strontium, and a trace of potassium. 



