and its Bearing on the Coral Reef Problem. 187 



which showed under the microscope small rhombohedra, diffi- 

 cultly soluble in II. CI. In the solution Mg was detected, but 

 the amount was too small for analysis. The anhydrite was 

 never completely converted and sometimes the reaction was 

 entirely absent, Similar results were obtained from a solution 

 of NaCl and anhydrite. Another reaction was that of MgCh 

 and NaCl on CaCO, under a pressure of 60-100 atmospheres 

 and a temp, from 4° to 14° C. A residue insoluble in 2 per 

 cent acetic acid was obtained, and in one case the residue had 

 the composition of dolomite. 



G. Linck,* by adding Am 2 C0 3 to a solution of Mg salts and 

 then adding Cad,, obtained first an amorphous precipitate, 

 which on long standing became small crystalline spherulites of 

 the composition of dolomite but having a + optical sign, and 

 decomposing when boiled with water. On heating these 

 spherulites with their mother liquor in sealed tubes for several 

 hours to 40°-50° C. the spherulites showed — optical sign and 

 only slowly dissolved in dilute acetic acid. The analysis showed 

 44 - 8 per cent of MgC0 3 which indicates an excess of MgC0 3 

 as compared with normal dolomite. Meigenf has repeated 

 these experiments, but has failed to obtain a precipitate of 

 similar composition. 



Phillipi£ disagrees with the views of Pfaff and agrees with 

 those of the writer that dolomite is formed in shallow water. 

 He instances the case of the calcareous nodules with dolomite 

 cement dredged from the Seine Bank N.E. of Madeira at a 

 depth of 150 meters. He argues that the dolomitization of 

 these nodules took place in shallow waters near the surface, 

 and that the bank has since then subsided, since at the present 

 depth not only is dolomitization not in progress, but solution 

 and disintegration of the nodules is occurring. 



Van Tuyl§ tried the effect of known concentrates of MgCl, 

 and MgS0 4 and of mixtures of the salts both with and without 

 the presence of NaCl on powdered aragonite. Tested after 

 six months and again after three years the results were nega- 

 tive. Attempts made by Van Tuyl to obtain dolomite as a 

 direct chemical precipitate by evaporating for a month solu- 

 tions of the bicarbonate of calcium and magnesium in molecu- 

 lar equivalent proportions, resulted in the separate precipitation, 

 first of CaC0 3 and later of MgC0 9 . Even when the solution 

 was inoculated with a crystal of dolomite the results were 

 negative. 



A careful consideration of the results of these experimental 

 investigations leads the writer to agree with the conclusions of 



*G. Linck, Moustsber Deutsch. Geo!. Ges., pp. 230-241, 1909. 



f Meigen, op. cit. 



jPhillipi, Neues Jatirb., Festbancl, pp. 397-445, 1907. 



«5 F. Van Tuyl, op. cit. 



