55 
TUSSOCK FORMATIONS. 
The rich soil of marshes, bogs and swamps usually furnishes 
these plants propagate has a marked effect upon the fate of the 
swamp. 
Such plants gain their first foothold in the shallower waters 
rd le tio I 
pro- 
Fic. 12.—T ks i h north of museum, now the bed of a lake. 
cowded stems, and as a consequence, the lodgment of dirt, and 
make solid ground of it. Meanwhile the nearby waters, made 
shallower by this same process, are in turn invaded, and the en- 
tire swamp occupied and filled up in course of time. Such ac- 
tion is shown by reeds and cattails. 
