374 
GEOGKAPHICAL DISTEIBUTION, 
Chap. XI. 
site sides of the world. But we have good evidence in 
almost every case, that the epoch was included within 
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 fiowering 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 
