1906] 



IN CHEMICAL GEOLOGY. 29- 



gestion, may be worth considering. The quantity of carbon dioxide 

 locked up within the Hthosphere is, as shown by the data now before 

 us, about equal to twenty-five times the mass of the atmosphere. 

 To that quantity must be added at least three more atmospheres, and 

 perhaps a much larger quantity of oxygen which has been con- 

 sumed in transforming the ferrous compounds of the igneous rocks 

 into the ferric oxide of the sediments. We may well ask whether 

 all of this material was actually absorbed from the atmosphere, and 

 if so, whence was it derived? Did the primeval atmosphere contain 

 it all at once, or was it drawn from cosmical sources, or expelled 

 first from the earth's interior? These questions I shall not attempt 

 to answer, for I do not care to enter the realm of speculation. It is 

 enough for me to point out the order of the quantities involved in 

 the problems thus suggested, problems which have been the themes 

 of many writers, and leave them as crude data for possible future 

 use. 



One other phase of geochemical statistics remains to be men- 

 tioned ; namely, the attempt to use chemical evidence in the measure- 

 ment of geological time. At least two such efforts have been made ; 

 the one by T. Mellard Reade,^ the other by Professor Joly.- ]\Ir. 

 Reade, from a study of the soluble substances contained in the sur- 

 face waters of England and Wales, estimates that their removal 

 from the rocks and soil would lower the level of those countries 

 at the rate of one foot in 12,978 years. This means a transfer ta 

 the ocean of dissolved matter alone equivalent to 143.5 ^^^'^^ P^^ 

 annum from each square mile of land ; and to this must be added 

 the solid sediments. From various data relative to the drainage 

 basins of Europe, and to some large rivers in other parts of the 

 world, Reade calculates that the average denudation of all the land 

 of the globe amounts to about 800 tons annually per square mile. 

 This figure, combined with the supposition that the sediments repre- 

 sent a thickness of ten miles, gives a period of 526,000,000 years 

 since the process of sedimentation began. The assumed thickness 

 is evidently many times too great, and the figure is, therefore, 

 excessive. 



^"Chemical Denudation in Relation to Geological Time," London, 1879. 

 ^ Sci. Trans. Royal Dublin Soc, ser. 2, vol 7, p. 23. Alsa a note in Chem^ 

 News, vol. 83, p. 301. 



