DED UCTION. ANTICIPA TION. 1 3 5 



Santa Cruz, and in a remarkable degree the 

 tufaceous formations at the northern end of 

 Chiloe. I was so much struck with this re- 

 semblance, that I particularly looked out for 

 silicified wood, and found it under the follow- 

 ing extraordinary circumstances." 1 



We are not told whether he gained his first 

 knowledge of the connection between silicified 

 wood and tufaceous formations from his geo- 

 logical researches in South America; nor if he 

 did, whether he had come to the general con- 

 clusion that silicified wood is likely to be found 

 in tufaceous formations, and therefore it ought 

 to be found in the beds of the Uspallata range, 

 or whether he simply reasoned that because 

 silicified wood is found in the tufaceous beds of 

 Chiloe, therefore it will be found in the very 

 similar tufaceous beds of the Uspallata range. 

 It is known that the two are found in connec- 

 tion in different parts of the world, and there 

 is a causal connection between them. The 

 peculiar conditions under which tufaceous beds 

 are deposited, and the subsequent processes of 

 mineral solution, etc., are such that, if wood 

 was present at the time of the deposition 

 of such beds, it would probably be silicified. 

 Whether Darwin knew of this causal connec- 



1 Geological Observations, etc., p. 526. 



