EARLY WORKS. 31 



passage in the work, maintain that he was convinced 

 of evohition. His great caution in dealing with so 

 tremendous a problem explains why the second 

 edition does not reflect the state of his mind at the 

 time of its publication. He tells us (" Autobiography ") 

 that in the preparation of this second edition he 

 " took much pains," and we may feel confident that 

 much of this care was given to the decision as to 

 how much he should reveal and how much withhold 

 of the thoughts which were occupying his mind, and 

 the conclusions to which he had at that time arrived. 

 That he did attribute much importance to the evolu- 

 tionary passages added in the second edition is shown 

 by his letter to Lyell (July, 1845), in which he alludes 

 to some of them, and specially asks Lyell to read the 

 pages on the causes of extinction. 



He also edited and superintended the " Zoology 

 of the Voyage of H.M.S. Beagle," the special parts of 

 which were written by various eminent systematists, 

 and appeared separately between 1839 and 1843. 



He also read several papers before the Geological 

 Society, including two (1838 and 1840) on the For- 

 mation of Mould by the Action of Earth- Worms — a 

 subject to which he returned, and upon which his 

 last volume (pubhshed in 1881) was written. He also 

 read a paper on the Parallel Roads of Glen Roy before 

 the Royal Society (published in the Phil. Troms., 

 1839). These wonderful parallel terraces are now 

 admitted to be due to the changes of level in a lake 

 following those of an ice-barrier at the mouth of 



