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, and 

 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 under 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 



