BOTANY OF LARIMER COUNTY 131 
istics of each of these formations and a representative list is given of 
species found in each. Probably the most interesting part of the paper 
is the account and discussion of the Cercocarpus Scrub Formation on 
the rock ridges. This formation is confined to rocky places and is 
replaced by grassland in the valleys. The line of contact between scrub 
and grassland is often very sharply marked. The controlling factor 
which determines the distribution of the scrub and grassland formations 
is the soil quality and not rainfall or temperature. A number of illus- 
trations are used to show the characteristic features of the region and 
the various formations studied. 
