Transactions of section c. 721 



disintegrate under tile energetic action of various acid gases, and atnong volcanic 

 exhalations sodium chloride has been especially noticed as abundant. Conse- 

 quently we find that while the proportion of sodium in Professor Joly's average 

 river water is only o'73 per million, in the rivers of the volcanic island of Hawaii 

 it rises to 24-5 per million.^ No doubt the area occupied by volcanoes is trifling com- 

 pared 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 consideration may be judged from the composition 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 difl'erent 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 Bodium to the ocean. Finally, 

 .ilthough 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 removed from the critical point. Water begins 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 ns seems to render some reduction in Dr. Joly's 

 estimate imperative. A precise assessment is impossible, but I should be inclined 

 myself to take ofl' 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 evidence .seems to suggest, more than 

 twenty -six millions of years must have elapsed during their formation. 



Obscure Chapter in the EarilCs History, 



Before discussing the validity of the argument on which this last result de- 

 pends let us consider how far it harmonises with previous ones. It is consistent 

 with Lord Kelvin's and Professor Darwin's, but how does it accord with Professor 

 Joly's ? Supposing we reduce his estimate to fifty-five millions : what was the earth 

 doing during the interval between the period of fifty-five millions of years ago and 

 that of only 26i millions ago, when, it is presumed, sedimentary rocks commenced to 

 be formed ? Hitherto we have been able to reason on probabilities ; now we enter 

 the dreary region of possibilities, and open that obscure chapter in the history of 

 the earth previously hinted at. For there are many possible answers to this 

 question. In the first place the evidence of the stratified rocks may have been 

 wrongly interpreted, and two or three times the amount of time we have demanded 

 may have been consumed in their formation. This is a very obvious possibiUty, 

 yet again our estimate concerning these rocks may be correct, but we may have 

 erroneously omitted to take into account certain portions of the Arcbrean complex, 

 which may represent primitive sedimentary rocks, formed under exceptional con- 



• Walter Maxwell, Lavas and Soils of the Hawaiian Islands, p. 170. 

 1900. 3 A. 



