756 



SCIENCE. 



[N. S. Vol. XII. No. 307. 



very materially affect our conclusions. The 

 total quantity of river water discharged 

 into the sea is, as we have stated, 6,524 

 cubic miles. The average composition of 

 this water is deduced from analyses of 

 nineteen great rivers, which altogether dis- 

 charge only 488 cubic miles, or 7.25 per 

 cent, of the whole. The danger in using 

 this estimate is two-fold : in the first place 

 7.25 is too small a fraction from which to 

 argue to the remaining 92.75 per cent., and 

 next, the rivers which furnish it are se- 

 lected rivers, i. e., they are all of large size. 

 The efiect of this is that the drainage of 

 the volcanic regions of the earth is not 

 sufficiently represented, and it is precisely 

 this drainage which is richest in sodium 

 salts. The lavas and ashes of active vol- 

 canoes rapidly disintegrate under the ener- 

 getic action of various acid gases, and 

 among volcanic exhalations sodium chloride 

 has been especially noticed as abundant. 

 Consequently we find that while the pro- 

 portion of sodium in Professor Joly's aver- 

 age river water is only 5.73 per million, in 

 the rivers of the volcanic island of Hawaii 

 it rises to 24.5 per million (Walter Max- 

 well, ' Lavas and Soils of the Hawaiian 

 Islands,' p. 170). No doubt the area oc- 

 cupied by volcanoes is trifling compared 

 with the remaining land surface. On the 

 other hand the majority of volcanoes are 

 situated in regions of copious rainfall, of 

 which they receive a full share owing to 

 their mountainous form. Much of the 

 fallen rain percolates through the porous 

 material of the cone, and, richly charged 

 with alkalies, finds its way by underground 

 passages towards the sea, into which it 

 sometimes discharges by submarine springs. 

 Again, several considerations lead to the 

 belief that the supply of sodium to the 

 ocean has proceeded, not at a uniform, but 

 at a gradually diminishing rate. The rate of 

 increase of temperature with descent into 

 the crust has continuously diminished with 



the flow of time, and this must have had 

 its influence on the temperature of springs, 

 which furnish an important contribution to 

 river water. The significance of this con- 

 sideration may be judged from the compo- 

 sition of the water of geysers. Thus 

 Geyser, in Iceland, contains 884 parts of 

 sodium per million, or nearly 160 times as 

 much as Sir John Murray estimates is 

 present in average river water. A mean of 

 the analyses of six geysers in different parts 

 of the world gives 400 parts of sodium per 

 million, existing partly as chloride, but 

 also as sulphate and carbonate. 



It should not be overlooked that the 

 present is a calm and quiet epoch in the 

 earth's history, following after a time of 

 fiery activity. More than once, indeed, has 

 the past been distinguished by unusual 

 manifestations of volcanic energy, and these 

 must have had some effect upon the supply 

 of sodium to the ocean. Finally, although 

 the existing ocean water has apparently 

 but slight effect in corroding the rocks 

 which form its bed, yet it certainly was not 

 inert when its temperature was not far re- 

 moved from the critical point. Water be- 

 gins to exert a powerful destructive action 

 on silicates at a temperature of 180° C, 

 and during the interval occupied in cooling 

 from 370 to 180° C. a considerable quantity 

 of sodium may have entered into solution. 



A review of the facts before us seems to 

 render some reduction in Dr. Joly's esti- 

 mate imperative. A precise assessment is im- 

 possible, but I should be inclined myself to 

 take off some ten or thirty millions of years. 



We may next take the evidence of the 

 stratified rocks. Their total maximum 

 thickness is, as we have seen, 265,000 feet, 

 and consequently if they accumulated at 

 the rate of one foot in a century, as evi- 

 dence seems to suggest, more than twenty- 

 six millions of years must have elapsed 

 during their formation. W. J. Sollas. 

 ( To ie concluded. ) 



