180 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 



tained. Dittmar states"^ that of 160 analyses of sea water collected by the 

 Challenger Expedition — 



Parts per thousand. 



The lowest (fioiu the southern part of the ludiau Oceau, south of 66° S. lat.) coutaineil 33 01 



The greatest (from the middle of the North Allautic, at ahout 23° N. lat.) contained 37.37 



Average 35. 19 



In general, therefore, we may assume 3.5 per cent, as the average of 

 total solids in sea water. 



Besides chlorine, sulphuric acid, calcium, magnesium, and sodium, 

 which make up ^^ of the total salts dissolved in the ocean, the investiga- 

 tions of Forchhammer and others have demonstrated the presence of 26 

 elements in solution, including bromine, iodine, flourine, phosphorus, 

 silicon, boron, silver, gold, copper, lead, zinc, cobalt, nickel, iron, manga- 

 nese, aluminium, magnesium, strontium and barium. Many of these are 

 present in extremely small quantities, and have only been detected by the 

 aid of the spectroscope ; while the presence of others has been determined by 

 indirect analysis. As methods of research become more refined, and larger 

 bodies of water are dealt with, it is to be presumed that more of the ele- 

 ments entering into the composition of the earth will be found dissolved in 

 the waters of the ocean. 



The following comparison of the composition of ocean and river waters 

 is from Roth's Chemical Geology ; the figures represent the mean of a large 

 number of analyses, and give percentages of total solids : 



Constituents. 



a. Carbonates . . 

 6. Sulphates 



c. Chlorides 



d. Other matter.. 



This comparison indicates the result of a very complicated series of 

 changes, dependent upon both biological and chemical reactions, which 

 occur when river waters are subjected to the process of concentration that 



"s Voyage of H. M. S. Challenger, Chemistry and Physics, Vol. I, p. 201. 



