312 BOTANICAL GAZETTE | MAY 
slopes gravity alone is sufficient, while on all slopes the trans- 
porting power of rain water comes into play. Usually at the 
foot of the hill and sometimes well up the slope the conditions 
are favorable for the climax society. Other hills (fg. 77) 

as 
catia oa” 

i 
Fic. 8.—Portion of an island near the one shown in figs. 6 and 7. Here the 
vegetation is further advanced. Besides lichens, etc., white and Norway pines are 
found. 
farther in the interior are completely covered with pine and 
deciduous forests. 
Vv. THE SWAMP SOCIETIES. 
One of the most characteristic features of a young glacial 
topography is the large number of lakes. In general these may 
be divided into two classes according to their mode of origin. 
One class is due to the action of the ice sheet. Depressions 

