156 FORMATION OF CORAL REEFS. 
the greater heights, till even these find a foot- 
hold no longer, and the summit of the moun- 
tain is clothed in perpetual snow and ice. What 
have we here but the same series of changes 
through which we pass, if, travelling northward 
from the Tropics, we leave Palms and Pome- 
granates and Bananas behind, where the Live- 
Oaks and Cypresses, the Orange-trees and Myrtles 
of the warmer Temperate Zone come in, anc 
these die out as we reach the Oaks, Chestnuts, 
Maples, Elms, Nut-trees, Beeches, and Birches 
of the colder Temperate Zone, these again waning 
as we enter the Pine forests of the Arctic bor- 
ders, till, passing out of these, nothing but a 
dwarf vegetation, a carpet of Moss and Lichen, 
fit food for the Reindeer and the Esquimaux, 
greets us, and beyond that lies the region of 
the snow and ice fields, impenetrable to all but 
the daring Arctic voyager ? 
I have thus far spoken of the changes in the veg- 
etable growth alone as influenced by altitude and 
latitude, but the same is equally true of animals. 
Every zone of the earth’s surface has its own 
animals, suited to the conditions uncer which 
they are meant to live; and, with the exception of 
those that accompany man in all his pilgrimages, 
and are subject to the same modifying influences 
by which he adapts his home and himself to 
all climates, animals are absolutely bound by 
