464 GEOGRAPHICAL DISTRIBUTION [Chap. VI 



Letter 352 if productions exactly fitted, not only for the climate, but 

 for all the conditions of the equatorial regions during the 

 Glacial period existed and could everywhere have immi- 

 grated. But the productions of the temperate regions would 

 have probably found, under the equator, in their new homes 

 and soils, considerably different conditions of humidity and 

 periodicity, and they would have encountered a new set of 

 enemies (a most important consideration) ; for there seems 

 good reason to believe that animals were not able to migrate 

 nearly to the extent to which plants did during the Glacial 

 period. Hence I can persuade myself that the temperate 

 productions would not entirely replace and exterminate the 

 productions of the cooled tropics, but would become partially 

 mingled with them. 



I am far from satisfied with what I have scribbled. I con- 

 clude that there must have been a mundane Glacial period, and 

 that the difficulties are much the same whether we suppose 

 it contemporaneous over the world, or that longitudinal 

 belts were affected one after the other. For Heaven's sake 

 forgive me ! 



Letter 353 To H. W. Bates. 



March 26th [1861]. 

 I have been particularly struck with your remarks on the 

 Glacial period. 1 You seem to me to have put the case with 

 admirable clearness and with crushing force. I am quite 

 staggered with the blow, and do not know what to think. 

 Of late several facts have turned up leading me to believe 

 more firmly that the Glacial period did affect the equatorial 



1 In his " Contributions to the Insect Fauna of the Amazon Valley," 

 Trans. Eniom. Soc, Vol. V., p. 335 (read Nov. 24th, i860), Mr. Rates 

 discusses the migration of species from the equatorial regions after the 

 Glacial period. He arrives at a result which, he points out, "is highly 

 interesting as bearing upon the question of how far extinction is likely 

 to have occurred in equatorial regions during the time of the Glacial 

 epoch." ..." The result is plain, that there has always (at least 

 throughout immense geological epochs) been an equatorial fauna rich in 

 endemic species, and that extinction cannot have prevailed to any extent 

 within a period of time so comparatively modern as the Glacial epoch in 

 geology." This conclusion does not support the view expressed in the 

 Origin of Species (Ed. I., chap. XL, p. 378) that the refrigeration of the 

 earth extended to the equatorial regions. (Bates, loc. cit., pp. 352, 353.) 



