758 T. C. BROWN OOLITES AND OOLITIC TEXTURE 



A B 



Si02 1.83 4.03 



Al,03 85 ) 



Fe^Oa 70 j- 



CaO 54.03 51.33 



MgO .72 



K2O, Na^O .63 



H2O (110° C.) .05 ) 



H,0 ) f 



CO2 [ 42.53 41.07 



SiOa .89 



Organic .27 



.20 



.83 



99.97 



A. Analysis of calcareous oolitic limestone from Waddle, Pennsylvania, by 

 W. A. Royee, of State College. 



B. Analysis of oolitic sand from Great Salt Lake, Utah, by T. M. Chatard. 

 (From U. S. Geological Survey Bulletin No. 491, page 533.) 



The oolites are somewhat variable in size, either spherical, oval, or rod- 

 like. The oval grains are generally larger than the spherical grains; the 

 spherical grains vary in diameter between .25 mm. and .75 mm., while 

 the oval grains are frequently over 1.00 mm. in length and the rodlike 

 grains as much as 2.00 mm. long. 



When examined in thin-section no nuclei of foreign material can be 

 seen. The majority of the grains have a comparatively coarse, radially 

 arranged fibrous structure. Some, possibly one-fifth of those in the 

 slide, have their center formed by a single large calcite crystal, generally 

 with polysynthetic twinning prominently developed. The sizes of these 

 central crystals show considerable variations. They are usually large, 

 having a diameter equal to at least one-half the diameter of the oolite; 

 in some cases the whole oolite seems to have been replaced by the calcite 

 crystal, while in other instances only a narrow zone of radially arranged 

 fibrous material is left near the outer edge of the oolite. Whenever the 

 radial structure is retained the oolites show a distinct dark cross between 

 crossed nicols (see plate 26, figures 5 and 6). 



The oolitic layers of limestone are the only layers that are distinctly 

 fossiliferous at this locality. Trilobites are the most abundant, but they 

 are very fragmentary. The fragments are so numerous, however, that 

 considerable difficulty was encountered in selecting a sample for the 

 analysis, which was in all probability free from such fragments. 



These oolites evidently formed where decaying organic matter was 

 abundant, and this material must have produced ammonium carbonate 

 in ample quantities to precipitate these oolites in the form of aragonite, 



