338 EDWARD STEIDTMANN 



merit of the development of dolomite in the sea as was urged 

 against the preceding group of experiments. The highest tem- 

 peratures of the sea, resulting from solar heating, on record are 

 those of the Red Sea 1 (31 C), and the Lagoons of the Celebes 



(32° C). 



3. FORMATION OF DOLOMITE AT ORDINARY TEMPERATURE AND PRESSURE 



By action of magnesium chloride and magnesium sulphate in 

 water on anhydrite in the presence of common salt and carbonic 

 acid (Pfaff, Jr., ibid., 557). 



By action of hydrogen sulphide in water on magnesium and 

 calcium carbonates, followed by the introduction of carbonic acid 

 (Pfaff, Jr., ibid., 556). 



4. FORMATION OF DOLOMITE AT ORDINARY" TEMPERATURE AND HIGH PRESSURE 



By the action of sodium carbonate on anhydrite in the presence 

 of common salt in a concentrated solution of magnesium sulphate 

 or chloride (Pfaff, ibid., 562). 



By the action of magnesium chloride or sulphate in a solution 

 of common salt on calcium carbonate. The speed of the reaction 

 is proportional to the degree of concentration of the solution 

 (Pfaff, ibid., 565). 



Pfaff 's experiments are highly creditable in that the replacement 

 of calcium carbonate by a magnesium salt so as to yield a product 

 approaching the dolomite ratio was effected without resort to high 

 temperatures. Doubtless other methods will yet be worked out 

 whereby this result can be obtained under conditions similar to 

 those prevailing in the sea. The last experiment by Pfaff is highly 

 suggestive when compared with the increase in the magnesium 

 content of marine oozes with depth; that is with pressure (see this 

 paper, p. 335). However, it does not seem safe to argue that 

 this has been a very important factor of control, since many 

 dolomites have very obvious earmarks of shallow-water deposition, 

 such as ripple marks, cross-bedding, and interstratification with 

 coarse sands. 



'Quoted by F. W. Pfaff, Neues Jahrb. Min. Beilage, XXIII (1907), 573. 



