THE NATURALIST AND COLLECTOR 
35 
as the tide of civilization has advanced. 
As a country becomes civilized some 
plants furnishing* food for varions an¬ 
imals have been destroyed and these 
animals were consequently compelled 
to seek new regions or eventually be¬ 
come extinct. Deserts act as barriers. 
Few animals can stand a journey across 
them, thus compelling different faunas 
on their opposite sides. Rivers some¬ 
times act as barriers, but often aid in 
the dispersal of small crustaceans, 
mollusus, etc. 
A most powerful means of dispersion 
is the ocean currents. By means* of 
great currents, seeds are carried onto 
various islands, and there growing, 
have developed a fauna where other¬ 
wise it would of necessity have been 
barren. The tropical marine animals 
sometimes follow the Gulf stream into 
climates, which were it not for this 
stream, would be almost artic, and here 
venturing to quit the stream,' lilave 
been merged insensibly into the range 
of other species 
Trade winds play an important part 
in scattering the minute forms of life. 
Whirlwinds and tornadoes often gather 
up small insects and transport them to 
other climates. Birds are sometimes 
blown off shore in wind storms, for 
hundreds of miles, and being unable to 
return have settled down and popu¬ 
lated the remote islands of the sea. 
Drift-wood often furnishes transpor¬ 
tation for small animals from shore to 
shore and also conveys seeds and vines 
which are upon it. Birds, when blown 
to distant islands often carry seeds in 
their crops, which soon develop a 
fauna upon which they feed. Darwin 
quotes a case where seeds have been 
disseminated by means of dry earth 
clinging to the feet of partridges. Many 
other cases of accidental or occasional 
means of dispersal are known, but the 
foregoing are the most prominent and 
most frequently seen. 
For convenience, the earth has been 
divided into various faunal districts 
The one expounded by C. Hart Mer- 
riam, of the U. S. Dept, of Agriculture 
and published in the annals of that 
department, is selected as being the 
most convenient, and is given below. 
He divides the country north of the 
tropics into six life zones, These are 
grouped under two heads: The North¬ 
ern or Boreal, and the Southern or 
Astral. In eastern North America, 
these zones are described as follows: 
The artic zone or the zone above 
the limit of tree growth, is character¬ 
ized by the dwarf willow, saxifrages, 
gentions, Artic poppy, etc., and by the 
snowy owl, snow bunting, polar bear, 
artic fox, and reindeer. 
The hudsonian zone, comprising the 
northern or higher parts of the great 
transcontinental coniferous forest, 
numbers among its inhabitants the 
wolverine, moose, great northern 
shrike, cross-bills, white-crowned spar¬ 
row, and fox sparrow. 
The Canadian zone, comprising the 
southern part of the coniferous forest, 
has among* its list of inhabitants the 
porcupine, red squirrel, var\ r ing hare, 
white throated sparrow, yellow rumped 
warbler, and many others. 
The transition zone, covering the 
northwestern part of the United States 
and part of Lanada has the oak, hick¬ 
ory, chestnut and walnut. Here the 
southern mole, the rabbit, oriole, 
thrush, catbird, bluebird, chewink, 
live in or near the haunts of the her¬ 
mit and Wilson’s thrushes, solitary 
Vires, bobolink, red squirrel, chip¬ 
munk, star-nosed mole, etc. The zone 
is one in which the outlying Boreal 
and Astral elements overlap and pro¬ 
duce a fertile agricultural region. 
