THE TERRANE AND THE RIVER SOLUTE 



155 



The Ordovician and Silurian rocks were therefore the first to he charged 

 with calcium carbonate shells and skeletons in large numbers. 



The hypothesis further states that not only a large part, if not all, of 

 the pre-Cambrian limestones and dolomites, but, as well, the limestones 

 and dolomites of the early Paleozoic formations, are chemical precipi- 

 tates thrown down by ammonium carbonate. This precipitation grew 

 slower in proportion to the development of the fishes and other efficient 

 bottom scavengers. When the scavenging system became well established 

 calcium salts could, for the first time, accumulate in the ocean water in 

 excess of the needs of lime-secreting organisms. Thereafter the marine 

 limestones have been largely formed from the debris of the hard parts of 

 animals and plants. 



The original paper contains a discussion of various tests of the sug- 

 gested hypothesis. These included, first, the witness of laboratory ex- 

 periments; secondly, the testimony of the Black sea — a basin where 

 modern limestone is being deposited by the organic alkali because of the 

 lack of a scavenging system over most of the basin-floor; and, thirdly, 

 the lithological evidence of pre-Cambrian sedimentary deposits. The 

 present paper is intended to suggest the value of additional evidence 

 based on the chemistry of the rivers draining pre-Cambrian terranes. 

 In addition, the testimony of the microscope to the chemical origin of 

 thick Cambrian and pre-Cambrian limestones is briefly outlined, and 

 the systematic chemical variation of the limestones through geological 

 time is quantitatively discussed. 



The Terrane and the Eiver Solute 



The influence of the kind of rock traversed by a river on the chemical 

 composition of that river is clearly illustrated by Hanamann's careful 

 investigation of the Bohemian rivers. 3 - His results are in part sum- 

 marized in the following table (I), in which the content of calcium and 

 the content of magnesium in streams issuing from different rock forma- 

 tions are given : 



Table I. 



Waters from- 



Granite 



Phyllite 



Mica-schist 



Basalt 



Cretaceous (partly limestone; 



Calcium in 



Magnesium 



Ratio of 



parts per 



in parts per 



calcium to 



million. 



million. 



magnesium. 



7 . 7.) 



2.33 



3.32 : 1 



5.72 



2.41 



2.37 :1 



9.33 



3 . 76 



2.48 : 1 



68.84 



19.7(5 



3.49 : 1 



133.38 



31.36 



4.25 : 1 



3 J. Hanamann : Archiv Natur. Landesdurchforschung Bohmen, vol. 9, no. 4, 1894 ; 

 vol. 10, no. 5, 1898 — quoted in F. W. Clarke's "Data of Geochemistry," Bulletin no. 

 330, U. S. Geological Survey, 1908, p. 79. Cf. also A. L. Ewing, American Journal of 

 Science, series iii, vol. 29, 1885, p. 29. 



