^0. 5 STUDY OF CHEMICAL DENUDATION — CLARKE 5 



In an essay of this kind it is impracticable to give all the details of the 

 liscussion. It is enough to indicate their nature briefly, for the results 

 ■an only be approximations to the truth, with no claims to finality. Tak- 

 ng the several continents in order, the composition of their waters tribu- 

 tary to the ocean may be estimated as follows : 



For the United States the data given by Dole and Stabler in Water- 

 supply Papers 234 and 236 are taken, together with those of Forbes and 

 >kinner for the Colorado. The river basins considered are the St. Law- 

 ■ence, Hudson, Delaware, Susquehanna, Potomac, James, Eoanoke, 

 STeuse, Cape Fear, Pedee, Santee, Savannah, Altamaha, Apalachicola, 

 Alabama, Pearl, Mississippi, Brazos, Colorado of Texas, Eio Grande, 

 :;:!olorado of Arizona, and Sacramento.' Each average composition is 

 roughly weighted proportionally to the total amount of dissolved matter 

 transported by the river in a year, and in that way the mean for the 

 United States is obtained ; a mean which is not likely to be much altered by 

 any future analyses. According to Dole and Stabler the quantity of saline 

 matter carried from these basins is 87 short tons or about 79 metric tons 

 per square mile annually. 



For the rest of North America only an estimate is possible. Eleven 

 analyses of river waters from the Saskatchewan system, one from the 

 Yukon, and one from the Ottawa, give a mean composition of the dis- 

 solved matter resembling that of the St. Lawrence. So much for British 

 North America and Alaska. For Mexican and Central American waters 

 no data are at hand, but it is probable that they would be, for northern 

 Mexico, at least, similar to those of Arizona, New Mexico and Texas. 

 That is, the waters north of the United States and south of it would vary 

 from the mean obtained for the United States, in opposite directions, 

 and so tend to balance each other. In short, the average for the United 

 States will probably represent fairly well the average for the entire con- 

 tinent. If we assume that six millions of square miles of North America 

 lose 79 metric tons in solution per square mile per annum, and that the 

 composition of the saline matter so transported is that found for the 

 United States alone, we shall not be very far from the truth. 



Analyses of South American river waters are not numerous. For the 

 great rivers north of the Amazon I have found no data at all. We may 

 assume, however, that they will resemble the Amazon in their general 

 features, and taking the analysis and denudation factor of that river as 

 typical, we can regard its composition as representing the waters of about 

 three millions of square miles. Figures for the Uruguay, draining 

 151,000 square miles, I have already given. There is also an analysis by 



1 Average of 20 composite analyses of 10 daily samples each, furnished by Mr. E. B. Dole. Not 

 in Dole's memoir. 



