CHEMICAL COMPOSITION OF RIVERS AND LAKES 



G39 



to an underestimate of chloride and perhaps of silica. 

 The remainder of Europe has been assumed to be like 

 that part drained by the principal rivers, and a weighted 

 mean leads to the result that about 110 metric tons 

 per square mile are carried away each year. This 

 is the highest rate of chemical denudation of any 

 continent. The figure may be lowered somewhat when 

 data become available for Mediterranean Europe, 

 but it does seem well established that the rate of denuda- 

 tion is high. This is probably due mainly to the moist 

 European climate, although the large areas of fine- 

 grained Pleistocene deposits may also be an important 

 factor. 



Table 76. — Discharge and chemical denudation of Europe 



ASIA 



Except for the U.S.S.R. and Japan, most of Asia 

 is hydrologically very little known. The estimate for 

 the discharge for the temperate parts of the Pacific 

 basins, shown in table 77, is close to the discharge rate 

 for the Amur, and intermediate between the rates for 

 the Yangtze and the Hwang Ho. The estimate for the 

 discharge rate of the tropical parts of Asia is inter- 

 mediate between the rates L'vovich gives for the 

 Malayan Archipelago and the Ganges. The most 



Table 77. — Discharge and chemical denudation of Asia 



uncertain part of the whole computation is the tropical 

 section, for here the figures for both discharge and 

 chemical content are of low reliability. They represent 

 a considerable improvement over the data available in 

 1924, however, and lead to an estimate of 83 metric 

 tons removed in solution per square mile of the Asiatic 

 landmass, a very respectable figure when one considers 

 the extensive areas of desert that contribute nothing to 

 the total. 



AFRICA 



There are no satisfactory analyses for any major 

 river of Africa, but many data which can be used in 

 estimating the chemical denudation. The basis for 

 such an estimate is shown in table 78. There are no 

 complete analyses for the Orange and the Zambezi, but 

 the Cunene and Limpopo are fair-sized rivers in the 

 same general part of Africa, and probably approach 

 them in chemical composition. The four rivers chosen 

 to represent the miscellaneous humid parts of Africa 

 have been chosen from among a much larger number of 

 analyses of rather dilute tropical waters. The major 

 rivers of Africa, taken by themselves, give a misleading 

 impression of the total runoff. A weighted mean of the 

 chemical composition of African rivers leads to an 

 estimate of 63 metric tons removed each year for each 

 square mile of total land surface. 



Table 78. — Discharge and chemical denudation of Africa 



AUSTRALIA 



Data on which to base an estimate of chemical 

 denudation for Australia are very scant. About one- 

 third of the continent lacks rivers flowing to the sea 

 and may be left out of computation. The perennial 

 rivers, for which there are numerous analyses, are 

 mostly very dilute. They are in regions of abundant 

 rainfall, flowing over rocks some of which are very 

 resistant to weathering and all of which have been 



