EVOLUTION OF LIMESTONE AND DOLOMITE 341 



COMPOSITION OF EXCELSIOR SPRINGS, MISSOURI' 

 Salinity 489 Parts per Million of Water, or about 0.4 per cent 

 Ca 29.28 

 Mg 3. 15 

 Co 3 55.92 

 Ratio of Ca to Mg 9.3:1 



The calcium carbonate of the ocean bottom is in contact with 

 a solution high in magnesium and low in calcium, largely derived 

 from the lands and not from the ocean bottom. The calcium 

 carbonate of the land areas is on the average, so far as humid 

 climates are concerned, in contact with carbonated waters high 

 in calcium and low in magnesium whose salts are derived from 

 the decomposition of the rocks through which they circulate. In 

 the light of experimental evidence, on the replacement of calcium 

 carbonate by magnesium carbonate, where are the conditions 

 more favorable for dolomitization by replacement, in the ocean or 

 in the sea of underground water? Of course there are analyses 

 of underground waters which show a high content of magnesium, 

 which could possibly cause dolomitization, but these seem to be 

 either exceptional or local. 



C. EVOLUTION VERSUS THE METAMORPHISM OF LIMESTONES AFTER 

 THEIR EMERGENCE FROM THE SEA AS EXPLANATION FOR THE 

 INCREASE IN THE RATIO OF CALCIUM TO MAGNESIUM OF LIME- 

 STONES AND DOLOMITES WITH GEOLOGIC TIME 



Evidence has been presented for both the development of dolo- 

 mite in the sea and its origin by the metamorphism of limestones 

 after their emergence from the sea. Magnesian limestones can 

 develop in the sea from a combination of organic and inorganic 

 processes. The known inorganic processes are direct chemical 

 precipitation, leaching, and secondary replacement. These may 

 also be effected through the agency of underground water. Evi- 

 dence has been presented to show that these processes are operative 

 in the sea on a much larger and more uniform scale because of the 

 chemical properties of the sea as compared with those of under- 

 ground water. Underground waters derive their dissolved mate- 

 rials from the rocks through which they circulate, and generally 



1 From Bull. 330, U.S. Geol. Survey, 150. 



