EVOLUTION OF LIMESTONE AND DOLOMITE 



419 



magnesium content of streams in arid climates tends to be high, 

 as shown by the following table. 



TABLE XXIV 



Calcium Magnesium Ratio in Streams of Arid Countries 



Streams 



Sacramento R., Cal 



San Lorenzo R., Cal 



Santa Clara R. ; Cal 



Mission Creek, Cal 



Cold Spring Creek, Cal 



Mono Creek, Cal 



Santa Ynez R., Gibraltar, Cal 



Chelif R., Algeria 



Chelif R., Algeria 



Chelif R., Algeria 



Brazos R., Tex 



Rio Grande, Tex 



Pecos R., N.M 



Colorado River, Yuma, Ariz. . 



Gila River, Ariz 



Salt River, Ariz 



Colorado R., Austin, Tex 



Rio Grande, Laredo, Tex 



Brazos, Waco, Tex 



Mg 



* Source 



Clarke, Bull. 330, U.S.G.S., 70 



70 

 70 

 70 

 7° 

 70 

 70 

 70 

 70 

 70 



69 

 69 

 69 

 69 

 69 

 69 

 W.S. Paper 236, U.S.G.S., 



96 

 50 



Where the terrane is exceptionally calcareous, however, cal- 

 cium may predominate considerably. The insolubility of lime 

 under arid conditions is illustrated by Hilgard's 1 composite soils, 

 Table XXV. 



TABLE XXV 



Calcium Magnesium Ratio in Soils from Arid and Humed Regions 



Soil 



Average of 466 soils from humid regions of southern part of 



United States 



Average of 313 soils from arid portions of United States 



Apparently soils in arid climates contain about twice as much 

 calcium in proportion to magnesium as those of humid climates. 



Influence of the belt of cementation on the calcium magnesium 

 ratio of underground waters. — The materials carried in solution 

 by underground waters in the belt of cementation undergo various 

 abstractions and additions on their way to the sea. The cements 



J E. W. Hilgard, Bull. No. 3, U.S. Weather Bureau (1892), 30. 



