374 GEOGRAPHICAL DISTRIBUTION, Chap. XI. 



the latest geological period. We have, also, excellent 

 evidence, that it endured for an enormous time, as 

 measured by years, at each point. The cold may have 

 come on, or have ceased, earlier at one point of the 

 globe than at another, but seeing that it endured for 

 long at each, and that it was contemporaneous in a 

 geological sense, it seems to me probable that it was, 

 during a part at least of the period, actually simulta- 

 neous throughout the world. Without some distinct 

 evidence to the contrary, we may at least admit as 

 probable that the glacial action was simultaneous on 

 the eastern and western sides of North America, in the 

 Cordillera under the equator and under the warmer 

 temperate zones, and on both sides of the southern 

 extremity of the continent. If this be admitted, it is 

 difficult to avoid believing that the temperature of 

 the whole world was at this period simultaneously 

 cooler. But it would suffice for my purpose, if the 

 temperature was at the same time lower along certain 

 broad belts of longitude. 



On this view of the whole world, or at least of broad 

 longitudinal belts, having been simultaneously colder 

 from pole to pole, much light can be thrown on the 

 present distribution of identical and allied species. In 

 America, Dr. Hooker has shown that between forty and 

 fifty of the flowering plants of Tierra del Fuego, forming 

 no inconsiderable part of its scanty flora, are common to 

 Europe, enormously remote as these two points are ; and 

 there are many closely allied species. On the lofty 

 mountains of equatorial America a host of peculiar 

 species belonging to European genera occur. On the 

 highest mountains of Brazil, some few European genera 

 were found by Gardner, which do not exist in the wide 

 intervening hot countries. So on the Silla of Caraccas 

 the illustrious Humboldt long ago found species belong- 



