192 HALL AND SARDESON — THE MAGNESIAN SERIES. 



Dittmar * found strikingly similar results. He calculated them differ- 

 ently ; Forchhammer ^ also. 



DiTTMAR. 



CI 100. 



22.561 



SO3 11.576 



CaO 3. 053 



MgO 11.212 



K2O 2.405 



NaaO 74.760 



Forchhammer. 



CI 100. 



O Equivalent not determined. 



SO3 11.88 



CaO 2.93 



MgO 11.03 



K,0 1.93 



Na20 Not determined. 



We see from the two series of investigations resulting in the above 

 figures that the quantity of the magnesium salts is practically four times 

 as great as that of calcium. 



Thus in ordinary dolomites, taking into account the quantity of mag- 

 nesium salts alone, the theory advanced by some that dolomite was 

 formed by the addition of magnesium carbonate is both plausible and 

 reasonable, provided the conditions were favorable for such addition ; 

 but it must be confessed that the writers have looked in vain for an 

 example among the sedimentary deposits of modern and Mesozoic seas 

 of such addition to the normal carbonate precipitates. 



Composition of modern Sea-deposits. — Looking over the results of several 

 investigations, we gather the following analyses of recently formed lime- 

 stone rocks. They show a very low proportion of magnesium carbonate 

 and other magnesium salts. Only the carbonate constituents of the 

 several examples are given : 



I. II. III. IV. V. 



CaC03 83.99 98.26 92.80 95.00 92.51 



MgCOs 1.04 1.38 1 2.38 1 5.00 2.45 



I. Analysis of coquina deposits at Saint Augustine, Florida. Charles P. Berkey, 

 University of Minnesota. 



II. Coral sand, straits of Balabac. Dana : Corals and Coral Islands, page 357. 



III. Chalk from an elevated reef of Oahu. Dana : Corals and Coral Islands, 

 page 358. 



* H. M. S. Challenger Reports : Physics and Chemistry, vol. i, p. 23 et seq. 



tAlgOs, 0.24. 



X Other substances, 4.82. 



