A PRELIMINARY STUDY OF CHEMICAL 

 DENUDATION 



By frank WIGGLBSWORTH CLARKE 



CHIEF CHEMIST U. S. GEOLOGICAX SUR1T:Y. 



In 1876 the late T. Mellard Eeade delivered a remarkable address 

 before the Liverpool Geological Society/ which was afterwards separately 

 printed nnder the title, " Chemical Denudation in Eelation to Geological 

 Time." In this address Eeade attempted to m.easure the solvent action 

 of surface waters in England and Wales, and to estimate the amount of 

 dissolved solids annually carried by British rivers to the sea. His con- 

 clusion was, in brief, that the annual run-off in England and Wales trans- 

 ported 8,370,630 toDS of mineral matter in solution; a quantity which 

 would represent a lowering of the area in question at the rate of one foot in 

 12,978 years. Evenly distributed, the amount of material so removed 

 from the land amounted to 143.5 tons per square mile of surface, a 

 figure which is surprisingly large. Eeade also, from such data as he 

 could obtain, made similar but rough estimates for several European 

 river basins; which, in British tons per square mile, may be tabulated as 

 follows : 



Rhone 232. 



Thames 149. 



Garonne 142. 



Seine 97. 



Rhine • • • 92.3 



Danube '^2. 7 



The average for the entire land surface of the globe he put at 100 tons 

 per square mile, a figure that was not much better than a guess. 



About eight years later, in another address before the Liverpool Society, 

 Eeade discussed the subject of denudation in the two Americas." For the 

 !\Iississippi, on the basis of a single old and imperfect analysis, he com- 

 puted a solvent lowering of the drainage basin at the rate of 120 tons per 

 square mile per annum and for the Amazon his figure was 50 tons. For 

 the St. Lawrence and the Eiver Plate liis figures are less explicit, but the 

 St. Lawrence he considers as having a greater chemical activity per square 

 mile than the Mississippi. His former average of 100 tons for all the 

 river basins of the globe he regarded as confirmed. 



1 Proc. Liverpool Geol. See, vol. S, p. 211, 1876. 



2 See " The Evolution of Earth Structures," pp. 255-282. London, 1903. 



Smithsonian Miscellaneous Collections, Vol. 56, No. 5 



