Hill: Penobscot Vegetation 411 



long to the type which originates through the filling in of a 

 water-filled depression. A second type of bog results from 

 the gradual building up of vegetation on a comparatively 

 flat surface. This is the raised bog so characteristic of the 

 Maine coast east of Penobscot Bay, and of the Maritime 

 Provinces (see Nichols, 23, 24). The sphagnums which 

 play the prominent part in the formation of such a bog re- 

 quire a very large amount of water, more than can be sup- 

 plied from the ground. This additional moisture is ob- 

 tained directly from atmospheric precipitation, a phenome- 

 non which gives the name of precipitation swamps to these 

 areas. In the course of the development of a raised bog 

 there is usually a more or less definite sequence of stages, 

 comprising a bog meadow, wet bog and dry bog, the latter 

 constituting the climax association. In the Penobscot Bay 

 region there is but a single instance of a bog which can be 

 undoubtedly attributed to the raised type and in this case 

 the vegetation has reached the dry bog stage. In the "Bog" 

 in Rockland the ground is covered with a compact growth 

 of the usual ericaceous shrubs with a few subordinate herba- 

 ceous species. The area covers over a square mile of terri- 

 tory and is about four feet higher in the center than near the 

 margins, thus exhibiting in its convex surface one of the 

 chief characteristics of raised bogs. Toward the northern 

 end it merges with a deciduous swampy wood while at the 

 southern edge the damming of a small stream which flows 

 out of the bog has altered the vegetation thereabouts to 

 such an extent that it exhibits the features of a filled-in bog 

 with a definite zone of aquatics and a sedge and shrub stage. 



d. Association-types of spring swamps 

 Many of the swamps in the Penobscot Bay region owe 

 their origin to the presence of seepage water from the 

 ground water table. These spring swamps may occur on 

 wet slopes along streams where they are subject to occa- 

 sional inundation, or at the edge of beaches. The latter 



