592 W. A. T_VEE CiOLITES IX SHALE A>'D THEIE ORIGIN 



iOTS millimeter (plate 22. figure 2). and the next is the outermost sphere. 

 which is quite translucent. There is a suggestion of a radial structure in 

 some of the oolites, but it disappears entirely under crossed nicols. 



All the large oolites and many of the small ones show a slight flatten- 

 ing, so that they have a somewhat elliptical form. The concentric spheres 

 are slighth* broken at the sides. In all the oolites the borders are not 

 distinct and sharply cut^ but are more or less irregular. 



There is no evidence of a nucleus in any of the oolites, and the sur- 

 rounding material is not disturbed in any way, showing that all growth 

 of the oolites had ceased before the consolidation of the material. A 

 striking feature of the rock is the development, on a microscopic scale, of 

 the structural feature called stylolites. Their description will be included 

 LQ a forthcoming paper on stylolites. 



THE OOLITES IX TEE GREEX SHALE 



The green shale is sandy, like the red shale, and contains more oolites 

 than either of the others, especially more of the large oolites. They show 

 the same tendency to aggregation, but are iii no way related to l>edding 

 planes or other structural features of the rock. 



The microscope shows that the oohtcs contain less sand than those in 

 either of the other shales. It is scattered throughout the rock as in the 

 other shales, and when an oolite contains one or more graios they are ia 

 no way related to the oolitic structiu'e, but occur in any portion of it, the 

 oolite having simply inclosed them. 



The diameter of the oolites averages slightly over .6 millimeter, while 

 occasionally there is one which has a diameter of nearly a millimeter. 

 The small oolites are about the same size as those in the other shales. 

 The numerous concentric rings of the oolites in the red and yellow shales 

 are missing in those of the green shale. There is one narrow, translucent 

 ring which is practically the same size in all the oolites — that is, .266 

 millimeter in diameter. This uniformity in diameter was noted in the 

 oolites of the other shales. This would hardly be expected, for the ma- 

 terials came from different portions of the formation, and, as already 

 noted, a characteristic feature of the beds is the abrupt variation in com- 

 position. The larger oolites and the smaller ones appear to be of about 

 the same average size in all the shales. 



Xumerous grains of calcite occur in the green shale and sometimes lie 

 partly within the oolites. These grains are very irregular in shape and 

 may occur in any portion of the shale. This distribution indicates that 

 the grains of calcite are not unchanged j^ortions left by a replacement of 

 calcite by silica, but that the calcite grains, like the sand grains, were 



