January joth, I go6.] PROCEEDINGS. xiii 



that is the fact that siUcates in which soda is the principal alkah 

 are, on the whole, more readily decomposed, both by hydro- 

 chloric acid and by the ordinary weathering processes of the 

 atmosphere, than the corresponding silicates containing potas- 

 sium. I have a list of some of the commoner silicates containing 

 sodium either as the principal or one of the principal alkalies, 

 and including such minerals as Albite, Natrolite, Nephelite, 

 Sodalite, Pectolite, &c., and out of 15 such minerals no less than 

 eight are decomposed by dilute hydrochloric acid, — one or two 

 only with difficulty, but most of them easily. The commoner 

 silicates containing potassium do not appear to be decomposed 

 anything like so easily. I should contend, therefore, that at the 

 first attack of the dilute acid of the primeval ocean upon the 

 silicates of the crust, those containing sodium would yield more 

 readily than those containing potassium, so that there would be 

 a greater amount of sodium chloride than of potassium chloride 

 in the sea from the very first. There is strong evidence that 

 such a preferential action has taken place in the well-established 

 fact that, whereas the average amount of soda in the igneous and 

 eruptive rocks is higher than that of the potash in the proportion 

 of about four to three, in the sedimentary rocks, which have 

 been derived from the igneous and eruptive rocks, the propor- 

 tion of soda to potash is only about three to five. Plainly the 

 soda has been much more completely dissolved out than the 

 potash. 



The paper gave rise to an interesting discussion, in which 

 several members took part. 



Ordinary Meeting, February 13th, 1906. 

 The President, Sir William H. Bailey, in the Chair. 



Dr. R. S. HuTTON and Mr. C. S. Allott, M.Inst.C.E., were 

 nominated auditors of the Society's accounts for the session 

 1905-1906. 



