3 
soil strongly affects the vegetable growth of a locality; as animal 
life of a locality is practically dependent on the vegetation it is in that 
way affected by the proportion of moisture present. The amount of 
moisture of a region is regulated by its distance from large bodies of 
water, the direction of the prevailing air currents, and the height of 
intervening obstacles, such as mountain ranges. Most of the mois- 
ture present in the air originates in the evaporation of seas and other 
large bodies of water. The moisture laden air moving inland when 
cooled is unable to hold up all its moisture, which falls as rain. A 
high range of mountains will greatly cool the air currents passing 
over it and the heavy rainfall or snowfall resulting may abstract so 
much of the moisture from the air, that little is left for the region 
beyond the mountains, which thus becomes arid. The region of 
the Colorado and Mojave Deserts and the greater part of Nevada is 
an illustration of the drying influence which the Sierra Nevada Moun- 
tains exert on the air currents passing over them. 
The quality of the soil is another factor in the quantity and 
character of the plant and animal life of a region. The carnivorous 
species of animals of a region subsist on the herbivorous species; 
these subsist on the leaves, stems, seeds or root of plants which 
draw their nourishment from the soil; therefore a richer or poorer 
soil has a considerable direct influence on such apparently remotely 
connected beings as the foxes or hawks that live in a region. 
Dr. C. Hart Merriman has formulated certain laws of the distri- 
bution of life which appear to be based on sound reasoning from a 
sufficient mass of observed facts to assure their correctness. 
“The northward distribution of animals and plants is determined by 
the total amount of heat—the sum of effective temperatures. 
The southward distribution of Boreal, Transition zone, and Upper 
Austral species is determined by the mean temperature of the hottest 
part of the year.” 
If the North Temperate Realm was composed of sea and level 
land only, its life zones would nearly follow parallels of latitude 
around the northern hemisphere, deflected here and there by the 
effects of warm or cold ocean currents on the shores they wash. 
The presence of mountain ranges breaks up such uniformity of clim- 
ate and renders the definition of life zones very difficult, nowhere 
more so than in California, where, in many mountains, island-like 
areas are detached from the main bodies of their zones or Yong 
