750 T. C. BROWN OOLITES AND OOLITIC TEXTURE 



by the water, the precipitation being due to one of the following causes: 

 (1) Cooling and consequent supersaturation of the solution (for exam- 

 ple, Carlsbad springs) ; (2) evaporation of water and consequent super- 

 saturation; (3) loss of excess of carbonic acid necessary to hold the car- 

 bonate in solution due to agitation of the water, to heating of the water, 

 or to some other cause. 



In all of the papers thus far mentioned one fact seems to have been 

 ignored which was clearly pointed out by Sorby as early as 1879, namely, 

 that all recent oolites consist of calcium carbonate in the mineral form 

 aragonite and not in the more common and stable form of calcite. Sorby 

 further pointed out that the spherical forms in the sprudelstein of 

 Carlsbad are not formed of radially arranged crystals of aragonite, with 

 their long axes in the radial direction, as would be expected if they 

 formed by the normal deposition of the minute crystals from solution, 

 but that the longer negative axes of the crystals are in reality tangential 

 to the little spheres. He explains this arrangement by saying that prob- 

 ably "the minute crystalline nuclei were mechanically accumulated 

 round a center, something like the layers in a large rolled snowball.^' ^^ 

 The mineral form aragonite never arises from supersaturated solutions" 

 of calcium carbonate under the ordinary conditions of temperature and 

 pressure which prevail in the sea and lakfe waters where oolites are form- 

 ing. This might have been used as a very strong argument in favor of 

 the organic origin of oolites because both plants and animals are able 

 to separate calcium carbonate from sea-water in this mineral f orm.^^ 

 But, so far as the writer knows, this argument was never advanced. 



Linck was the first to attack the origin of oolites from the experimental 

 point of view and produce oolites artificially under conditions which 

 probably very closely approach those which obtain in nature where these 

 structures are forming.^* He found that in all recent occurrences of 

 oolite which he was able to examine the grains consisted of aragonite, 

 while in the older or "fossil" oolites they consisted of calcite. He there- 

 fore concluded that all oolites were first formed as aragonite and later 

 changed to calcite, a suggestion previously made by Sorby.^^ 



Linck therefore set to work to produce oolites artificially in the labo- 

 ratory. By experimenting directly with sea-water and certain precipi- 

 tating reagents, he found that he could produce oolites that agreed with 

 natural oolites in every detail. Sodium carbonate and ammonium car- 



" H. C. Sorby : Ann. address. Geol. Soc. London, 1879, p. 74. 



1^ See Sorby, loc. cit. ; also W. Meigen : Centralb. f. Min. Geol. u. Pal., 1901, pp. 

 577-578. 



1* G. Linck : Neues Jahrb. f. Min. Geol. u. Pal., BB. XVI, 1903, pp. 495-513. 

 "Loc cit, p. 75. 



