222 Rhodora [DECEMBER 
years ago concluded from observations on wharves at Boston, that 
there had been a sinking of two feet during the past century.” In 
view of this statement, the presentation of new evidence concerning 
subsidence in the Cape Cod district seems to be justified. 
Before discussing either the formation of salt-marshes or the question 
of subsidence, it will be necessary to describe in brief the topography 
of the region about Woods Hole, and, rather more in detail, certain 
features in the historical development of the Chamaecyparis bogs which 
are found there. 
Woods Hole lies at the southern extremity of the basal lobe of Cape 
Cod, on the Falmouth continuation of the Plymouth moraine. ‘The 
glacial drift is for the most part very coarse, and readily permeable to 
water. The water table is reached at slight depths. Northward 
from the village the surface is characterized by a number of kettle 
holes,— steep-walled depressions in the till supposed to have been 
formed by the melting of isolated masses of buried or imbedded ice 
after the recession of the ice sheet. These are occupied either by ponds 
or by Chamaecyparis bogs, and are, of course, undrained. Their 
vegetation was described several years ago by C. H. Shaw.! Although 
his paper gives a good idea of the present flora of the bogs, it is inac- 
curate in so far as it relates to their development. 
The typical ice-block hole has steep sides, and, comparatively 
speaking, а flat bottom. ‘The vegetation which occupies it belongs to 
one of four types, which are determined by the relation of the water 
table to the surface of the ground. 1) The water table is far enough 
below the ground surface so that the mesophytic vegetation of hill- 
sides and valleys becomes established. This condition is uncommon 
about Woods Hole because the water table is very close to the surface. 
2) The water table practically coincides with the floor of the depres- 
sion, so that conditions favor a hydrophytic vegetation. In holes of 
this type Chamaecyparis bogs have developed. 3) The water table 
intersects the ground level on the gently sloping floor of the hole. 
In this case there is a shallow pond at the center, with an annular 
area around it, where, as in a hole of the last type, the water table 
is near the surface of the ground and conditions are favorable for 
Chamaecyparis. 4) The water table intersects the steep sides of the 
depression. Here there is no habitat favorable for Chamaecyparis. 
! The Development of Vegetation in the Morainal Depressions of the Vicinity of Woods 
Hole. Bot. Gaz. xxxiii, (1902) p. 437. 
