124 Reviews — J. Joly^s Aye of the Earth. 



I^ :e "v I :h3 aat s. 



I. — An Estimate of the Geological Age of the Earth. 

 By J. JoLY, M.A., B.A.I., D.Sc, F.K.S., F.G.S., M.E.I.A., 

 Hon. Sec. Key. Dublin Soc, Professor of Geology and Mineralogy 

 in the University of Dublin. Scientific Transactions of the 

 Eoyal Dublin Society, ser. ii, vol, vii (1899) ; 4to, pp. 44. 



rpHE paper consists of an introduction and these nine sections : — 



I. The estimate of geological time. 

 II. The original condition of the ocean. 



III. The supply of sodium by the rivers. 



IV. The saline deposits. 



V. The alkalies of the rocks. 

 YI. The potash of the rivers. 

 VII. Uniformity of denudation by solution. 



VIII. The alkalies of sediments, and the geological age of the latter. 

 IX. The solvent denudation of the ocean. 

 And two appendices. 



Appendix 1 is generally useful. It contains a list of numerical 

 quantities adopted in the calculations. Appendix 2 is a list of 

 sources of error which may modify the conclusions. 



The matters treated of in the nine sections are epitomized in the 

 introduction. 



The first point argued is, that so much of the removal of the 

 land surface as is due to solution may be accepted as a uniformitarian 

 process ; and this being granted, if we take the one element of 

 sodium, which is dissolved out of the rocks and enters the ocean 

 through river discharge, and if we assume that there was no sodium 

 in the primseval ocean, the amount of sodium in the ocean divided 

 by the amount annually brought down by rivers will give the 

 length of time during which the accumulation has been going on, 

 and will be a measure of the age of the world. 



Professor Joly claims that the amount of sodium in the ocean 

 agrees very well with that which must have been lost by the 

 crystalline rocks in the process of their being converted into the 

 existing volume, as usually estimated, of the sedimentaries. This 

 would decidedly support his view that the sodium of the ocean 

 has been derived from the crystalline rocks, and that the primitive 

 ocean was devoid of that element. 



I. The data upon which the calculations are made are as follows : 

 " The absolute masses of the ingredients of the ocean " are : 



Tons. 

 Sodium chloride 35,990 x lO'^. 



Magnesium chloride 

 Magnesium sulphate 

 Lime sulphate . . . 

 Potassium sulphate 

 Magnesium bromide 

 Lime bicarbonate 



5,034 X 10'2. 



2,192 X 10>». 



1,666 X 1012. 



1,141 X 10'2. 



100 X 1012. 



160 X 1012. 



