16 The New York State College of Forestry 
age has been established adjacent to Hard Wood Island. 
(Figure 1.) The intercepting barrier at this poimt has 
been cut away by a wide channel quite down to the river 
level. It is interesting to note as bearing on the causes of 
vegetation types that about the head of this established drain- 
age and quite within the bog area, thickets of alder replace the 
bog vegetation proper. It is assumed that this difference is 
associated with the freer drainage. 
In order to emphasize the role which edaphic factors play 
in determining types of vegetation, we may specify three 
edaphic units as follows: (1) The flat undrained sand plain; 
(2) The low, but well drained sand mounds and ridges inelud- 
ing the eskerlike ridge. (3) The flood plain of Grasse river. 
Of these, only the first bears any relation to the development 
of bog vegetation though all constitute features of the Grasse 
tiver Marsh as locally known. It must be borne in mind 
also that while historically considered the origin and early 
course of vegetation on the low sand plain is the most import- 
ant aspect of the problem of the development of vegetation with 
which we are here dealing, at the present time this originally 
flat, undrained substratum of sand is covered by a blanket of 
peat, and that this peat substratum rather than the original 
sand substratum determines the plant associations which form 
its present vegetation cover. In describing the relation of the 
present vegetation to edaphic conditions, therefore, we shall 
speak of the peat beds rather than of the original wet sand plain. 
The Peat Beds of the Grasse River Sand Plain 
The main area of the sand plain on the east side of Grasse 
River and abutting on Massawepie Lake and outlet and Town 
Line Pond is covered with a peat blanket varying in thickness 
from more or less eighteen inches at the south end to seven or 
eight feet over the center of the north east third of the bog.* 
The smaller section of the plain west of the river appears to 
be covered with a rather uniform depth of peat averaging about 
* At the southern end of the marsh the peat becomes very shallow and 
finally disappears as the sand bed rises into the bordering eskerlike ridge. 
