L86 K W. Sh'ats — Tin Formation of Dolomite 



E. W. Skeats, Bull. Mas. Oomp. Zool., Harvard 1903, pp. 



58-126. 

 \Y. Meigen, Sonderabdruck, Geo!. Rundschau, Leipzig, Bd. i, 



pp. 12 I -120, 1910. 

 Steidtmann, Jour. Geol., pp. 323-45, 392-428, 1911. 



F. W. Clarke, Data of Geochemistry, Bull. 330, U. S. Geol. Sur. 



20, pp. 480-490, 1908. 

 F. M. Van Tuyl, this Journal, xlii, 249-260, 191G. 



A study of the mode of occurrence of dolomites among the 

 older limestones was undertaken by the writer to see if the 

 independent evidence of associated organisms or characteristic 

 structures would throw any light on the conditions of the 

 formation of dolomite, and the result has been to substantiate 

 the view of its formation in shallow water. The object of this 

 communication is to review some of the experimental work on 

 the formation of dolomite, to correlate the evidence of its dis- 

 tiibution among recent and upraised coral limestones, and to 

 bring together some geological facts of distribution bearing on 

 the conditions of formation of the mineral, and finally to indi- 

 cate the bearings of the conclusions drawn from these various 

 lines of enquiry, upon the conditions of formation of the atoll 

 of Funafuti among other coral islands. 



Experimental eoidence of the formation of dolomite. 



The literature on this subject has been summarized by Pfaff* 

 and Steidtmann. f Marignac, Durocher, C. Saint Clair Deville, 

 A. von JVIorlot, and T. Sterry Hunt, among others, claimed to 

 have formed dolomite experimentally by various processes 

 generally involving great heat and considerable pressure. It is 

 not, however, always clear in -the case of these early researches 

 whether the product was a mixture of calcium and magnesium 

 carbonates or the definite mineral compound dolomite. Elem- 

 ent's experiments showed that aragonite organisms and aragon- 

 ite heated in a closed tube with a concentrated solution of 

 magnesium sulphate at G0° C, readily took up magnesium car- 

 bonate to the amount of 41 - 5 per cent of MgC0 3 , while calcite 

 was but little affected. The product, however, was a mixture 

 of the two carbonates and not the definite compound dolomite. 

 Pfaff,:}: as the result of certain experiments, claims that the 

 formation of dolomite in nature occurs at great depths and 

 pressure. He treated powdered anhydrite (gypsum gave nega- 

 tive results) in a concentrated solution of MgCl, 2 containing 

 NaCl, to the action of Na 2 C0 3 for a long time under pressure, 

 and got a residue, difficultly soluble in 5 per cent acetic acid, 



*F. W. Pfaff, N. Jahrb., Beit. Bd. xxiii, p. 529, 1907. 

 ■j- Steidtmann, op. cit. 

 \ Op. cit. 



