EVOLUTIONAL GEOLOGY. 303 



More than once, indeed, has the pa.st been distinguished bj- unusual 

 manifestations of volcanic energy, and these must have had some effect 

 upon the supply of sodium to the ocean. Finally, although the exist- 

 ing 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 us seems to render some reduction in 

 Professor Joly's estimate imperative. A precise assessment is impos- 

 sible, but I should be inclined m3^self to take off some ten or thirty 

 millions of 3"ears. 



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 the}^ accumulated at the rate of 1 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 EARTh's HISTORY. 



Before discussing the validity of the argument on which this last 

 result depends, let us consider how far it harmonizes with previ(5us 

 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 fift^^-five njillions; what was the earth doing during the 

 interval between the period of fifty-five millions of 3^ears ago and that 

 of only twenty-six and one-half millions of years ago, when, it is pre- 

 sumed, sedimentary rocks commenced to be formed? Hitherto vre 

 have been a})le to reason on probabilities; now we enter the dreary 

 region of possibilities, and open that ol^scure 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 })een wrongly interpreted, and two or three times the amount 

 of time we have demanded may have been consumed in their forma- 

 tion. This is a very obvious possibility, yet again our estimate con- 

 cerning these rocks may be correct, but wc may have erroneously 

 omitted to take into account certain portions of the Archa'an com- 

 plex, which may represent primitive sedimentary rocks, formed under 

 exceptional conditions, and subsequently transformed under the influ- 

 ence of the internal heat of the earth. This, I think, Avould be Pro- 

 fessor Bonney's view. Finally Lord Kelvin has argued that the life 

 of the sun as a luminous star is even more briefly limited than that of 

 our oceans. In such a case if our oceans were formed fifty -five millions 

 of years ago it is possible that after a short existence as almost boil- 

 ing water they grew colder and colder till they became covered with 

 SM 1900 22 



