EVOLUTION OF LIMESTONE AND DOLOMITE 415 



as approximating the composition of the primitive lithosphere. 

 In tracing the evolution of the limestones and dolomites to chemi- 

 cal changes in the sea, it is found highly probable that the ratio 

 of calcium to magnesium in the streams is higher at the present 

 time than in the streams of the primitive lands. This will develop 

 from the following considerations. 



The influence of the terranes on the calcium magnesium ratio of 

 underground water and streams. — Unfortunately the data on the 

 calcium magnesium ratio of streams and underground water 

 cannot be regarded as a satisfactory basis for correlation with 

 the calcium magnesium ratio of the terranes over which they flow. 

 The chances of error in water analysis and the variability of the 

 composition of streams make a single analysis or even a group of 

 analyses a questionable basis of correlation. The yearly average 

 stream compositions based on daily samples gotten by the United 

 States Geological Survey 1 for the streams of the United States 

 east of the 100th meridian constitute a creditable exception. 



Judging by the data available, it seems that underground 

 waters and streams have a higher ratio of calcium to magnesium 

 than the terranes through which they flow. This agrees with the 

 fact that the metamorphism of rocks results generally in a higher 

 percentage loss of calcium than of magnesium. From Orton's 2 

 figures, the average ratio of calcium to magnesium in the Niagara 

 limestone of Ohio is 1.72. The rock waters as reported by Orton 

 in the Niagara limestone have the following ratios of calcium to 

 magnesium : 



LOCALITY Ca/Mg 



Sidney, Ohio 4.0 



Celina, Ohio 1.92 



Fountain Park, Ohio 3 ■ * 5 



Fountain Park, Ohio 2.52 



Plain City 2.55 



Harrisburg 2 . 59 



An average of 66 analyses of well waters from sandstones given 

 in Bull. 4, of the University of Illinois, yields a ratio of calcium 



1 R. B. Dole, "Water Supply," Paper 236, U.S.G.S. 



2 Edw. Orton, Nineteenth Ann. Rept. U.S.G.S., Part 10. 



