420 



George E. Nichols, 



head better than under any other, swamps which are quite com- 

 monly encountered along the shores of well-drained lakes. 

 Locally along the margins of these lakes (Fig. 6i) there have 

 been formed broad, nearly level beaches, sometimes twenty-five 

 or fifty feet in width, which lie somewhat above the level of 

 the lake in summer, but are submerged during winter and early 

 spring, at times when the outlet is blocked up by the ice. 



At an early period in its development the vegetation in such 

 an area is essentially as described for the beach in connection 



Figure 6i. — Small, well-drained lake with border of marshy swamp: 

 mountains north of Barrasois River. 



with the vegetation of well-drained lakes and ponds (p. 417) : 

 an open swamp association of a pioneer type. In the course of 

 time, under favorable conditions, the more or less discontinuous 

 plant cover characteristic of this early stage may become con- 

 tinuous. Largely through the activity of the sedges, Carex 

 filiformis, Carex oligosperma, and Rynchospora alba, a shallow 

 layer of peat is formed and the level of the swamp's surface 

 is gradually raised higher. It is worthy of special note that the 

 sphagnums play a relatively insignificant part in the building up 

 process : the cushion-forming species so conspicuous in bog 



