58 
perate life floor. . : 
e Middle Temperate life zone for the most pait forms belts 
manifestly extensions of the treeless region above, should be called 
Alpine or Frigid, 
PLANT FORMATIONS. 
plant life is substantially the same. This may be due to the con- 
dition of the soil, such as the various alkaline formations of which 
the Salt Lake formation is the most conspicuous, but it is gener- 
ally due to differences of climate ard isolation. For example 
