356 Proceedings Portland Society Natural History 



consist of such species as Festuca rubra, Poa compressa, 

 Rosa humilis, Aquilegia canadensis, Myrica carolinensis, 

 Rhus Toxicodendron and various annual weeds. Lichens 

 are frequent on these abrupt, sheltered shores and they com- 

 prise species like Verrucaria maura and Verrucaria mucosa 

 growing where they are submerged at high water; Verru- 

 caria nigrcscens, just above the upper limit of the tides and 

 Lecanora subfusca var. campestris, Lecidea coarctata, 

 Lecanora cinerea, Lecanora atra, and Rhizocarpon confer- 

 voides anywhere above the limit of the highest tides. 



In more exposed localities the action of sea, wind, and 

 other factors have altered conditions and resulted in the for- 

 mation of definite sea bluffs and headlands along eroding 

 shores ; and beaches of various sorts along depositing shores. 

 The coastline of the Penobscot Bay region is so diversified 

 that there is a great intermingling of these two types of 

 shore. It may be said in general, however, that eroding 

 shores are characteristic of salients, while depositing areas 

 occur in reentrants. 



a. Association-types of eroding areas along the coast 

 Association-types of rocky sea bluffs 



Along the outer shores of the islands and the more ex- 

 posed portions of the mainland sea bluffs have been de- 

 veloped by the action of the waves. These vary greatly in 

 height, some extending but a few feet above the sea, while 

 others tower to a height of several hundred feet as in the 

 case of the cliffs on Isle au Haut and Monhegan. The veg- 

 etation of the sublittoral zone at the base of the bluffs, 

 where the rocks run out beyond the low tide mark, consists 

 of various red, green, and brown algae with a profuse 

 growth of kelps in the deeper water. 



In the littoral zone between the low and high tide levels 

 the rocks are covered with masses of rockweed, species of 

 Fucus and Ascophyllum (Figure 17). While these are 

 perhaps more abundant near the low tide mark they may 



