HYDROGENIC OOLITES 337 



are, however, regarded by Rothpletz as of algous origin (see be- 

 yond). Linck (2,3:498) has obtained for these recent oolites an 

 aragonite reaction, while the fossil oolites are by him referred to 

 calcite. 



Linck (33:50(5) has experimented with the chemical precipita- 

 tion of lime from artificial sea water with results leading to the fol- 

 lowing conclusions : 



The maximum solubility of calcium carbonate in sea water is 

 about 0.0191% CaCOg. If this maximum is exceeded deposition 

 of CaCOg occurs, in the form of calcite in temperate climates and 

 of aragonite in tropical climes, but without the formation of 

 sphseruliths. The same thing is true of solutions of calcium car- 

 bonate otherwise free from salts. If the calcium sulphate of the 

 water is precipitated as carbonate by sodium or ammonium car- 

 bonat"^, it is always aragonite and of sphserulithic form. These re- 

 agents will precipitate calcite from solutions of calcium sulphate 

 otherwise free from salts, both at 40° C. and at 18° C. The solu- 

 bility of aragonite is thus shown to be greater in solutions which 

 are poor in or free from other salts than in those rich in such 

 salts, and that it is greater in colder than in warmer solutions. For 

 calcite just the reverse holds true, and hence, at a given tempera- 

 ture, sea water will hold in solution more calcium carbonate than 

 fresh water, but there may be circumstances under which arago- 

 nite and calcite are soluble in equal degree, and so may be formed 

 simultaneously. Both calcium carbonate and calcium sulphate are 

 more readily soluble in sea water than in fresh water. Applying 

 his results to the elucidation of the question of the origin of 

 marine oolites, Linck finds that the under saturation of sea water 

 precludes deposition of lime without the intervention of a precipi- 

 tating reagent, and this he finds in the sodium and ammonium car- 

 bonate resulting from the decay of organic matter. The precipi- 

 tated material is usually in the form of sphaeruliths or concretions 

 of aragonite with or without an inner grain. The latter is found in 

 the neighborhood of coasts, where the lime is deposited around 

 fragments of shells or coral, grains of quartz or other sand, foram- 

 inifera, etc., while in the open sea they are without central kernel. 

 Linck considers that all oolites and pisolites are of inorganic or 

 chemical origin, and that, whenever organic remains occur in the 

 mass, these are mechanically enclosed, or, in the case of unicellular 

 algse, the oolite grains serve as a basis for attachment. In the 

 open sea the sphcxruliths sink to the bottom in time, while near the 

 shore they are piled up into sand dunes and assorted, according to 

 size, with more or less mechanical wear. In the course of time the 



