128 Eevietvs — J. Joli/'s Age of the Earth. 



times past from what it is now, but attributes tbe deficiency of 

 potash in the ocean to a continual abstraction of that alkali in 

 deposits which have always been, and still are, going on upon the 

 sea bottom, especially in the form of glauconite. Moreover, while 

 the soda brought by rain from the ocean is returned to it again, 

 much of the potash is retained by vegetation, and finally deposited in 

 the strata. 



[Is it certain, however, that the primaeval ocean did not contain 

 soda ? If it did, the excess would be at once explained.] 



VII. The uniformity of denudation by solution throughout 

 geological time is a first requisite of Professor Joly's calculation. 

 The objection which would be probably made is, that the sodium 

 supply by rivers will have been greater in early times. To meet 

 this he first argues for a nearly equable distribution of land and sea 

 all along, so that there would not have been formerly much larger 

 areas exposed to denuding agency than now. This portion of the 

 present section is very interesting from a geological point of view, 

 and is well reasoned. No claim is made to settle definitely the 

 ratios of rainfall during successive epochs. 



In the next place the author meets the possible objection, that 

 it might be thought that formerly greater areas of the land surfaces 

 were occupied by crystalline rocks, which, containing a larger 

 percentage of sodium than the sedimentaries, would have supplied 

 that element at a quicker rate. In later times the sedimentaries 

 would occupy a larger proportion of the exposed surface, but the 

 balance of supply would, he thinks, be rectified by the greater ease 

 with which the sedimentaries, aided by disintegration into soils, 

 yield up the alkalies they contain. 



VIII. In this section " a very interesting but difficult line of 

 enquiry is suggested in the probable facts of geological denudation " 

 referred to in the previous section. The object in view appears to- 

 be to support the theory of uniformity of sodium supply. 



IX. By " the solvent denudation of the ocean " is meant its 

 action upon the coastlines. This is believed by the author to be 

 small compared with what goes on upon land surfaces. Moreover, 

 experiment has shown that sea- water has little efi'ect in decomposing 

 felspars, and similarly the volcanic products which are so abundant in 

 deep-sea deposits have the alkali ratio of igneous, not of sedimentary 

 rocks — " a plain proof that the waters of the ocean do not afi'ect 

 them as would terrestrial rain and rivers." The correction on the 

 world's age on account of the solvent denudation of the ocean will 

 be sufficient if half a million years is allowed. The final conclusion 

 is that " our present knowledge of solvent-denudation of the earth't' 

 surface points to a period of between eighty and ninety millions of 

 years having elapsed since water condensed upon the earth, and rain 

 and rivers and the actions continually progressing in the soils began 

 to supply the ocean with materials dissolved from the rocks." 



As Major Dutton has somewhere remarked, " If we enquire of 

 Mother Earth her age her face is the face of a sphinx." Has 



