THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 125 
prevent the mingling of their land faun to any extent, while 
they may have most of their marine species in common. Such 
cases are numerous; at the Galapagos, for instance, none 
of the truly land species are known to occur in any other 
region, while a large portion of the marine species are found 
also on the American coast. Temperature is undoubtedly 
the most effective cause in limiting the diffusion of land and 
fresh water, as well as marine animals; but its influences 
are much obscured by those of humidity, and by the varying 
character of soils, waters, and the resulting vegetation. 
Temperature, as a result of or combined with topography, 
forms a very effective force in limiting the distribution of 
land animals. High and continuous mountain ranges pre- 
sent an almost impassable barrier to the migration of most 
species. Thus the physical features which separate faunæ 
from regions east and west may be so strongly marked, that 
they more than counterbalance the climatic effects of lati- 
tude. In North America, the faunæ on the east of the 
Rocky Mountains are very different from those on the west, 
and the inclosed central table-lands are occupied by still 
different faunæ. The birds of Arizona resemble those of the 
table-land of Mexico rather than those of California or of 
exas. These physical features even effect a change in the 
migrations of the birds of this region; many of the birds of 
the Colorado valley, instead of migrating far to the north 
in summer, turn to the east and breed in the region north 
of Fort Whipple.* 
Climatic influences, almost alone, limit the distribution of 
mountain vegetation ; and, through the vegetation, more than 
directly that of mountain animals. The narrow limits within 
which mountain species are restricted show very plainly the 
effect of climatic influences. Among the butterflies of the 
White Mountains of New Hampshire, the abundant Chiono- 
bas semidea Edw., is restricted to the loftiest summit, never 
Stes y E. Coues, Prodrome of a work on the Ornithology of Arizona Territory, moped 
NATURALIST, Vol. I, p. 209. 

