298 T. M. Reade—Denudation of the two Americas. 
This is the mean denudation, but I have also shown that the 
denudation is very much equalized by the fact of the harder 
rocks usually occurring in areas of great rainfall. 
It is therefore not unlikely that, if we were to institute accu- 
rate experiments over a sufficiently long time, it would turn out 
that the calculation of the amount of matter removed in solu- 
tion could be verified by direct tests, and that even these hard 
rocks would be found to waste at something near the indicated 
rate. It would appear from the examples of the Mississippi, 
the Nile and Danube that the matter brought down in solution 
and suspension is as 1 to 3. 
ese examples are of rivers where there have been the most 
accurate and fullest data to judge by. Whether the propor- 
tion would be borne out in other river basins we have no very 
good means of judging; but it would appear that in large rivers 
the nature of the rocks is so varied, the areas being so exten- 
sive, that the relation of the materials in solution to those in 
red clay, which I suggest is. more likely to be the “dust of 
continents,” than to arise from the disintegration of volcanic 
matter, such as pumice, but it is no doubt largely mingled 
with such volcanic matters as Mr. Murray clearly shows. It 
seems to me rather a far-fetched notion that the winds shoul 
contribute dust to the deepest ocean, but that the waters should 
make no mechanical contribution to the deposit. The bulk of 
* Chemical Denndation. 
+ It is singular that Hutton in his theory of the earth estimates at a gross 
computation ‘ that the fourth of the solid land is composed of matter which bad 
formed the calcareous tests of animals ” 
+ Challenger Reports. 
