"Vol. 65.] ANNIVERSARY ADDRESS OF THE PRESIDENT. ciii 



total quantity of sodium given in tons by the total number of cubic 

 miles of river-water, amounts to 12,410 tons, or a little more 

 than one half of Joly's number (24,100), and thus gives for the 

 duration of time about twice the amount found by him, that is 

 about 175 millions of years. Considering that the Amazon, with a 

 volume which contributes more than half of the total quantity of 

 river-water stated above, is not credited with any sodium at all, I 

 think we may admit that this result approaches a superior limit. 



A good deal of interest attaches to the silicic acid of the river- 

 water. It might, indeed, provide us with a check on the sodium- 

 estimates, were it not for two circumstances. In the first place, a 

 large amount of this constituent is extricated from solution by 

 organisms, and used by them in the formation of their skeletal 

 parts. From its source to its termination, every freshwater stream 

 is constantly being robbed of its silica by diatoms and sponges. 

 The surveys of the freshwater planctone recently commenced may 

 enable us in the future to make an approximate allowance for this 

 loss ; at present, all we can say is that it is very great. The 

 second difficulty lies in the fact that we are not yet sufficiently 

 acquainted with the nature of the reactions which take place in the 

 weathering of silicates, and in particular, we are without data as to 

 the amount of soluble silicic acid which is liberated on their de- 

 composition. Nevertheless, an enquiry based on these admittedly 

 imperfect data may not be altogether without profit. Some interest- 

 ing relations arc obvious on inspection of Table V. The Mississippi 

 and the rivers of the eastern coast of North America are much 

 richer in silica than in sodium : as a curious coincidence, the ratio 

 in the case of the St. Lawrence and the Mississippi is very nearly 

 the same, about 1:5; in the rivers of the west these relations are 

 reversed, except in the case of the Sacramento. In the Snake river 

 silica appears to be wholly absent. On the other hand, the 

 Mohawk, and the Amazon (Table VI), which are devoid of sodium, 

 except that combined with chlorine, contain a very considerable 

 amount of silica. 



The average amount of silica, reckoned as SiO.„ in the rivers of 

 North and South America, may be calculated from Tables V & VI. 

 It amounts to 56,830 tons per cubic mile. 



Is it possible to discover how much sodium might upon a 

 reasonable expectation have accompanied this silica, when both 

 were set free from the parent silicates ? Let us attempt to answer 

 this question. 



