Postelsia 71 
acteristic rocky back beach is found only along 
one end of the lake. At the rate which this 
body of water is filling in, it is only a question 
of time when the three zones shall have been 
pushed so far out that what is now the back 
beach zone shall have yielded its place to the 
myacdime. forest. Lhe present tenants oi the 
rocky ledges may be able to maintain their foot- 
hold even after the forest has become estab- 
lished in front, yet new conditions of light and 
illumination will eventually tend to bring about 
a change. The plants dwelling upon this type 
of rocky beach constitute a Rosaceous shrub 
society, of which the principal species are: 
Spiraea menziesii Rubus s pectabilis 
Rubus parviflorus Neillia capitata 
Together with these occur Vaccinium par- 
vijolium and a few herbaceous forms like Poly- 
stichum munitum, Adiantum pedatum, etc. 
In the non-rocky back beach, there are re- 
gions which correspond to those of the mid and 
front beaches with reference to elevation and 
soil composition. Along the sandier, elevated 
portion the composition is shghtly more diver- 
