Alfred Russel Wallace 



every bed of every formation should have once extended over 

 the whole area of all the land of the globe ! The deposition 

 in narrow belts along coasts of all the matter brought down 

 by rivers, as proved by the Challenger, leads to the same 

 result. In my " Island Life," 2nd Edit., pp. 221-225, I have 

 discussed this whole matter, and on reading it again I can 

 find no fallacy in it. I have, however, I believe, over- 

 estimated the time required for deposition, which I believe 

 would be more nearly one-fortieth than one-twentieth that of 

 mean denudation; because there is, I believe, also a great 

 overestimate of the maximum of deposition, because it is 

 partly made up of beds which may have been deposited 

 simultaneously. Also the maximum thickness is probably 

 double the mean thickness. 



The mean rate of denudation, both for European rivers 

 and for all the rivers that have been measured, is a foot in 

 three million years, which is the figure that should be taken 

 in calculations. — Believe me yours very truly, 



Alfred K. Wallace. 



' To Prof. Meldola 



Parkstone, Dorset. April 27, 1897. 



My dear Meldola, — ... I thought Eomanes' article in 

 reply to Spencer was very well written and wonderfully clear 

 for him, and I agree with most of it, except his high estimate 

 of Spencer's co-adaptation argument. It is quite true that 

 Spencer's biology rests entirely on Lamarckism, so far as 

 heredity of acquired characters goes. I have been reading 

 Weismann's last book, " The Germ Plasm." It is a wonder- 

 ful attempt to solve the most complex of all problems, and is 

 almost unreadable without some practical acquaintance with 

 germs and their development. — Believe me yours very faith- 



^^^^J* Alfred R. Wallace. 



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