752 T. C. BROWN OOLITES AND OOLITIC TEXTURE 



that it separates from a very hot spring water poorer in salt but richer 

 in sodiiim carbonate than the sea-water. The mimerons dolomitic oolites 

 and iron oolites he considers secondary, derived from original aragonite 

 oolites by reactions with solutions of magnesium carbonate or iron car- 

 bonate. 



The experimental work of Linck on laboratory material has been cor- 

 roborated by the recent researches of Drew and Yaughan on the forma- 

 tion of oolites in the calcareous deposits around Florida and the Baha- 

 mas. Drew has shown that denitrifying bacteria play an important part 

 in bringing about the chemical conditions necessary for the precipitation 

 of the calcium carbonate, and Yaughan has shown that in these chemi- 

 cally precipitated muds oolites develop, often forming after the muds 

 are precipitated.^^ 



Thus we see that oolites are either organic, produced by algae, as advo- 

 cated by Eothpletz, or chemically formed by precipitation, as suggested 

 by Linck and observed by Yaughan, the precipitating reagents probably 

 being sodium carbonate or ammonium carbonate. 



In the remainder of this paper I shall attempt to show that in vll 

 American occurrences of oolite which I have been able to study the for- 

 mation of the oolites can be explained by the latter process, and that I 

 think it is the only process by which they are formed. 



Oolites from Gb^jat Salt Lake, Utah 



It was long ago recognized by geologists of the United States Survey 

 that oolitic sand is now forming in certain localities along the shore of 

 the Great Salt Lake. Gilbert recorded this occurrence in his monograph 

 on Lake Bonneville,^^ and several other Avriters have described it either 

 from studies in the field or from investigations of the (x.lites obtained 

 there. As already noted, Eothpletz studied these oolites both in the 

 field and in the laboratory. He found that three types of oolites occur — 

 round spherical or oval grains about one-third of a millimeter in diam- 

 eter; long cylindrical grains, generally about half a millimeter long and 

 one-tenth millimeter in diameter, and larger irregular tuberculated 

 forms several millimeters in diameter. These oolites had a radially 

 fibrous and concentric structure, and when obtained beneath the water 

 were coated with minute algae, while the grains from the shore when dis- 

 solved in very dilute hydrochloric acid yielded the dead and crumpled 

 cells of algae. 



" T. Wayland Vaughan : Jour. Wash. Acad. Sci., vol. iii, pp. 302-304. Carnegie Inst. 

 Wash., Pub. 133, pp, 173-177 ; also Year Book No. 10, pp. 149-154. 



^ Lake Bonneville, Mon. I, U. S. Geological Survey, 1890, pp. 169, 252. 



