XXIV] SIR CHARLES LYELL 421 



would also be transported occasionally by floating trees 

 carried down by floods. I think myself, however, that it is 

 most likely they were carried by the earliest canoes of pre- 

 historic man, and that they afford an example of rapid change 

 of specific form, owing to the ancestral species having been 

 subjected to a great change of conditions, both as regards 

 climate and food, and having had an immense area of new 

 country to roam over and multiply in, in every part of which 

 they would be subjected to different conditions. These con- 

 siderations, I think, fully meet the facts, and there ought to 

 be no large rodents found in the caves of Australia, and no 

 other rodents of very distinct type from those now living. 

 When any such are found it will be time enough to consider 

 how to account for them. It is, as you say, a most important 

 fact that, in three such distinct localities as New Zealand, 

 Australia, and Mauritius, no bones of extinct carnivora or 

 other mammalia should be found along with the wingless 

 birds and marsupials, while abundance of remains of these 

 groups are found. We may, I think, fairly claim this as a 

 proof that such placental mammals did not exist in those 

 countries, and the fact that the only exception in the existing 

 Australia fauna are mice indicates very clearly that they are 

 a recent introduction. When all the known facts are in our 

 favour, I do not think we need trouble ourselves to answer 

 objections and overcome difficulties that have not yet arisen, 

 and probably never will arise." 



Some months later (November, 1867) he wrote me about 

 the dispersal and the colours of the races of man. On the 

 first point I replied at some length, principally to show why 

 we should not expect the primary regions which show the 

 great features of the distribution of birds, reptiles, and mam- 

 malia should also apply to man. On the question of colour 

 I replied as follows : " Why the colour of man is sometimes 

 constant over large areas while in other cases it varies, we 

 cannot certainly tell ; but we may well suppose it to be due 

 to its being more or less correlated with constitutional cha- 

 racters favourable to life. By far the most common colour 



