474 



ROLLIN D. SALISBURY 



mile, which represents approximately the amount of salt brought to 

 the sea per year by rivers, assuming that the specific gravity of salt 

 is the same as the average specific gravity of the mineral matter in 

 solution in the sea and rivers; while 77.758 per cent, of the total 

 amount of mineral matter of the sea (4,532,110 cubic miles) is 3,524,- 

 078 cubic miles, the approximate amount of salt in solution in the sea 

 water. This amount divided by 0.0095 * s m ore than 370,000,000, 

 which represents roughly the number of years it would take for the 

 amount of salt now in the sea to have been brought to it by rivers, 

 at the present rate. 



This figure is, however, not to be taken as representing the age 

 of the sea. There are several reasons for avoiding this conclusion. 

 These are as follows: (1) The rate at which salt has been brought 

 in by rivers has probably not been constant; (2) the salt may have 

 been derived partly from sources other than land waters; and (3) 

 much salt has been extracted from the sea water and deposited. 

 The second and third points tend to offset each other. In spite of 

 the limitations imposed by these considerations, the figure 370,000,000 

 may give some conception of the order of magnitude of the number 

 which expresses the age of the sea in years. 1 



The calcium carbonate carried to the sea by rivers in solution, 

 at the present time constitutes, according to Table II, nearly 43 per 

 cent, of all the mineral matter taken to the sea in solution. Its 

 amount is therefore about one-fifth of a cubic mile per year. The 

 calcium carbonate now in solution in sea water represents but 

 o . 00345 of the mineral matter which the sea contains. This fraction 

 of 4,532,110 cubic miles is about 15,635 cubic miles, which represents, 

 approximately, the amount of calcium carbonate now in solution in 

 the sea. If this substance is carried to the sea at the rate of one- 

 fifth of a cubic mile per year, it would take only about 84,000 years 

 for the amount now in solution in the sea to be brought down 

 from the land. If the calcium sulphate of the sea water has been 

 derived partly from the calcium carbonate brought to the sea, this. 



1 Professor Joly has calculated, from the salt of the sea, that the time since the 

 ocean began to receive solutions from the land may be 90 to 100 millions of years. 

 He assigns 10 per cent, of the sodium chloride of the rivers to atmospheric sources. 

 {Transactions of the Royal Society of Dublin, Vol. VII (Series n), 1899, p. 23, and. 

 Geological Magazine, 1900, p. 220.) 



