6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



Schoeller of water from the Eio ISTegro, which I assign equal weight with 

 that of the Uruguay. The data for the River Plate are unsatisfactorj', 

 for the analyses suggest a strong probability of tidal contamination. 

 Soutli of the Plate the streams show a resemblance to those of our own 

 southwestern areas, of which the Colorado is the type. I have averaged 

 together twelve analyses, including two Chilean rivers, and so obtained tlie 

 results given in the following table. In combining the analyses they are 

 weighted as indicated at the foot of each column. 



COs 



so 



CI 



N03 



Ca 



Mg 



Na 



K 



Fe^Oa, AI2O3. 

 SiOa 



Weight 



This mean I shall assume as representing the waters of four millions 

 of square miles, with a denudation factor, as shown by the Amazon, Uru- 

 gua}^, and, for comparative purposes, the Colorado also, of 50 tons per 

 square mile annually. This is only a rough estimate, but it is a probable 

 one and the best I can make with the existing material. The Amazon 

 dominates the combination, just as the Mississippi does in the United 

 States. Data relative to the IMagdalena, Orinoco, Demerara, San Fran- 

 cisco, and Plate, the latter at some point far above the possibility of tidal 

 contamination, are much to be desired. 



Analyses of European river waters are abundant, but rarely numerous 

 enough for any one stream to give conclusive evidence as to its denudation 

 value. I have, however, averaged together 300 analyses of European lakes 

 and rivers,^ first by groups and then weighting each group proportionally 

 to its drainage area. In that way I have obtained a highly probable mean 

 for the composition of the waters, which will appear in a table to be given 

 later. The denudation factor I can only estimate rouglily. According 

 to Geikie " the Thames carries in solution past Kingston 5 18,330 British 

 or 550,930 metric tons dissolved inorganic matter annually. The drainage 

 area is 6100 square miles; hence a denudation factor of 91.3 tons; an esti- 

 mate much lower than that of Eeade. For the Meuse above Liege, the 



^ Not 300 rivers. Some streams, like the Elbe .ind Danube, are represented by numerous analyses. 

 = Text -book of Geology, 4th ed., vol. 1, p. 4S9. 



