126 Revieios — J. Joh/s Age of the Earth. 



potash, and soda as clilorides. The atomic percentages of Clarke's 

 average are given by himself as follows : — 



Iron 4-71 "1 



Calcium ... 3-53 | take up 



Magnesium ... 2-64 i- units of 



Potassium ... 2-35 [ chlorine 



Sodium ... 2-68 " ; 



Having given the composition of the crust, the author next 

 considers how the chlorine of the heated hydrochloric acid, which 

 he supposes then to have been in the ocean, would have been 

 distributed among the bases. 



It is evident that any sodium which was obtained by rock solution 

 from the floor of the primseval ocean must be deducted from that 

 supplied by the rivers, otherwise the age of the world will be 

 reckoned too long. Professor Joly proposes to estimate the former 

 by considering the chlorine in the ocean. Of whatever chlorine 

 there was in the primitive ocean the sodium would take 14 per cent, 

 (reckoning from the proportion of sodium to the other bases in the 

 crust). But some chlorine is also supplied by the rivers, and by rain 

 upon the land. He allows for this at a guess 10 per cent. Deducting 

 this, the total supply by rivers is 97-8 X 10" tons of sodium chloride 

 per annum. There are other chlorides (lithium 16 x 10^, ammonium 

 %-5 X 10") in the rivers. Thus we find 76 x 10^ tons of chlorine 

 discharged into the ocean annually by rivers. 



" If we assume that the final result as to the duration of denuda- 

 tion will not be far from 86 X 10'^ years, we arrive at a total 

 deduction of 6,536 x 10^- tons [of chlorine] as a correction on the 

 amount of chlorine contained [at present] in the sodium chloride of 

 the ocean." This, however, seems to postulate the period of 86 x 10'' 

 years, which is the thing to be found. The calculation will be — 



Tons. 



Chlorine in the sod. chl. now in the ocean 24,155 x 10^^ 



Chlorine in the mag. chl. now in the ocean 4,161 x lO^^ 



28,316 X 1012 

 Deduct chlorine introduced by rivers in 86 x 10^ years ... 6,536 x 10^* 



21,780 X 1012 



" The result is 21,780 X IQi- tons " of chlorine in the original 

 ocean. Of this, 14 per cent, will have been combined with sodium 

 as already explained, the remainder combining with the other bases 

 of the magma. This gives 1,972 x 10^^ tons of sodium in the 

 original ocean. Hence we have — 



Tons of sodium in the present ocean 15,627 x IQi* 



Tons of sodium in the original ocean .. . ... ... 1,972 x IQi* 



Difference given as brought in by rivers 13,655 x IQi'' 



This, divided by the annual supply of sodium by rivers, viz. 

 15,724 X 10^ tons, gives as a final result 86-8 x 10" years for the age 

 of the world. 



III. In this section some slight modifications of the supply of 



