PHYSIOGRAPHY OF THE SEA-SHORE 21 



Sea - water. — Osborn (19 18) has summarised the 

 opinions of a number of writers regarding the ocean 

 and its waters. Among other points of interest he quotes 

 the computations of T. Mellard Reade, J. Joly, Sollas, 

 and Becker and Clarke, from which it is inferred that the 

 age of the ocean since the earth assumed its present 

 form is somewhat less than 100,000,000 years. " The 

 63,000,000 tons of sodium which the sea has received 

 yearly by solution from the rocks has been continually 

 uniting with its equivalent of chlorine to form the salt 

 (NaCl) of the existing seas. So with the entire present 

 content of the sea, its sulphates as well as its chlorides 

 of sodium and of magnesium, its potassium, its calcium 

 as well as those rare chemical elements which occasion- 

 ally enter into the life compounds, such as copper, fluorine, 

 boron, barium — all these earth-derived elements were much 

 rarer in the primordial seas than in those of the present 

 time. Yet from the first the air in sea- water was much 

 richer in oxygen than the atmosphere. As compared with 

 primordial sea-water, which was relatively fresh and free 

 from salts and from nitrogen, existing sea-water is an 

 ideal chemical medium for life. As a proof of the special 

 fitness of sea-water to life processes we have the remarkable 

 resemblance in composition between the chemical composi- 

 tion of the chief body fluid of the highest animals, namely, 

 the blood serum, and that of sea- water " (see Henderson, 



1913). 



Composition of Sea-water. — While it is easy to deter- 

 mine the total solids in sea-water, the percentage determi- 

 nation of the individual constituents is a matter of great 

 difiiculty. At the present time oceanographers agree in 

 considering sea-water as a solution in which the individual 

 constituents are always present in the same relative propor- 

 tions, no matter how the degree of concentration may vary. 

 Consequently, in any given sample, once the quantity of a 

 single chemical constituent has been determined, e.g. chlo- 

 rine, the proportion of the other substances maybe calculated. 

 For this purpose use is made of Knudsen's tables, in which 



