28 



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



the sea, and the ordei- of magnitude to be ascribed to an allowance for the 

 latter, are briefly considered in tlie paper, as well as other questions which 

 arise. 



When all corrections arc made and the requisite latitude of error taken into 

 account, it would appear that the consideration of solvent-denudation, points to 

 an Age for the Earth, dating from the settlement of water upon its surface, of 

 between SO and 90 millions of years. 



I. — The Estimate of Geological Time. 



On the basis that the ocean possesses an average dejith of 2000 fathoms, and 

 occupies -j-V of the area of the globe, its total mass is calculated to be 1'322 x 10'* 

 tons.* Its ingredients in solution are : — 



100-000 



and the total salts are approximately 3*5 per cent, of the mass of the whole. 



On these data, the absolute masses of the ingredients of the ocean are 

 calculable : — 



35990 X 10" tons. 



46283 



Of the sodium chloride, 39 '32 per cent, is sodium. In the sea, there is, 

 therefore, a mass of sodium in solution amounting to 14,151 x 10'- tons. 



Sir John Murray,! ^^ the result of the analyses of 19 rivers — many of which 



* Encycloptedia Britannica — Article, " Sea." The analyses are Dittmar's from the Eeports of the 

 " Challenger" Expedition. 



f Scottish Geographical Magazine, 1887, p. 76. 



