ox THE GEOLOGICAL AGE OF THE EARTH. 379 



(deducible from our knowledge of the mean igneous rock-crust) which is 

 to be accounted for between what is now represented in the ocean by the 

 chlorides and what remains over in the detrital sedimentaries. Upon 

 making the calculations, we find that the sum of the soda in the ocean 

 and in the sedimentaries would nearly suffice to effect the full restoration 

 of this constituent to the original rock. There is not quite enough. 



The bulk of the siliceous sedimentaries is assumed to be represented 

 by a layer 1-77 kilometres deep spread over the land area. This on a 

 specific gravity of 2-5 affords a mass of 64 x lO^*"' tonnes, which we assume 

 to be 67 per cent, of the mass of the parent rock.'- Hence the parent rock 

 possessed a mass of 95-5x10"^ tonnes. We restore to this the soda 

 equivalent of the sodium now in the ocean, 21 '0 x lO''^ tonnes. The 

 mean soda- content of these sedimentaries determined on the analyses of 

 over one hundred typical siliceous sedimentary rocks given in Professor 

 H. Rosenbusch's Elemente cler Gesteinslehre (Stuttgart, 1890) is found to 

 be 1-47 per cent. This affords 9-4x10'^ tonnes in the layer 1-77 kilo- 

 metres thick. Restoring this also, the parent mass of igneous rock is 

 found to have possessed 3-20 per cent, of NaoO. According to Mr. 

 F. W. Clarke {loc. cit.), the mean igneous rock contains 3-61 per cent, of 

 soda. 



This approximate agreement between the amount of sodium in the 

 ocean and that missing from the sedimentary rocks is a confirmation of 

 the validity of the present mode of deducing the age of the earth. It is 

 directly opposed to the assumption of an ocean primevally charged with 

 sodium salts. The negation is the more emphatic, seeing that the loss 

 revealed by the sedimentary rocks of geological time appears to be 

 more than sufficient to account for what sodium is to-day in the sea. 



't, 



Planlion and Physical Conditions of the English Channel. — Second 

 Report of tJie Committee, consistinij o/ Professor E. Ray Lankester 

 (Chairman), Professor W. A. Herdman, Mr. H. N. Dickson, and 

 Ml. IV. Garstaxg {Secretary'), apfointed to mal-e Periodic Investi- 

 ijations of the PlanJdon and Physical Conditions of the EnglisJi 

 Channel during 1899. 



The series of periodic surveys for which provision was made at the Bristol 

 and Dover Meetings has been completed by Mr. Garstang, under the same 

 conditions as were described in the First Report of the Committee. Since 

 the Dover Meeting two surveys were carried out, viz., in November 1899, 

 and in the first week of March 1900, thus making five quarterly surveys 

 altogether. 



It has been found impossible to finish the examination of the large 

 quantity of material collected in time for report at the Bradford Meeting. 

 The Committee therefore desire to be reappointed (without a grant) in 

 order that they may present their final report at the Glasgow Meeting. 



Merrill, lac. cit. pp. 209-225. 



