NO. 5 STUDY OF CHEMICAL DENUDATION — CLARKE 7 



figures published by Spring and Prost ^ give a factor of 139 tons per square 

 mile. Eeade's estimate for all Europe is 100 tons, and that seems to be 

 fairly probable. For Europe, then, I shall assume that 3,000,000 of square 

 miles suffer solvent denudation at the rate of 100 tons per mile, a figure 

 which is much like that of the St. Lawrence. Europe is generally well- 

 watered, and its waters have all the characteristics of those from the humid 

 areas of the United States. In the latter the denudation factor is lowered 

 by the arid regions of the southwest. 



The African material is very scanty. In addition to the figures already 

 cited for the Nile, with a drainage area estimated at 1,293,050 square 

 miles, I have found only analyses of three small Algerian rivers which 

 exhibit all the peculiarities of waters from other semi-arid districts. 

 Ignoring the latter I shall estimate that 1,-500,000 square miles in Africa 

 are represented by the Nile with the denudation factor of 16 tons. I 

 shall also assume that 6,500,000 square miles are fairly equivalent in 

 character to South America, with the same composition of the waters and 

 the same denudation factor of 50 tons. The desert regions, like the Sahara, 

 of course count for nothing. Analyses of water from the Niger, Congo, 

 Orange, and Zambesi are much needed. 



The data relative to x\siatic waters are still more defective. I have 

 found analyses by Schmidt of water from Lake Baikal and the river Om 

 in Siberia, and one by Nicholson, of the Mahanuddy in India. Waters of 

 saline lakes, not tributary to the ocean, I of course leave out of account. 

 The water of Lake Baikal is closely similar in character to that of the 

 Yukon and St. Lawrence; that of the Mahanuddy more resembles the 

 waters of tropical South America. With these feeble clues I can only 

 make a very rough estimate for Asia, as follows : Assume three millions 

 of square miles to average like Europe; three millions like the United 

 States; and one million like South America. I.iarge areas in Asia ob- 

 viously are left out of consideration ; the Caspian depression, the deserts of 

 Cfentral Asia, and the Arabian peninsula. The streams which reach the sea 

 from Arabia are too insignificant to carry any weight in the general dis- 

 cussion. For Australia I have no data. 



To sum up, the crude figures upon which to base further discussion are 

 as follows, beginning with a summary of the denudation values for each 

 continent : 



North America 6,000,000 sq. miles, at 79 tons. 474,000,000 tons 



South America 4,000.000 " " "50 " 200,000,000 " 



Europe 3,000,000 " " "100 " 300,000,000 " 



Asia 7,000,000 " " "84 " 588,000,000 " 



Africa 8,000,000 " " "44 " 352,000,000 " 



Total 1,914,000,000 " 



1 Ann. Soc. G§ol. Belg., vol. 11, p. 123. 



