Hill: Penobscot Plants. 203 



resulting- from the lava tlow of old volcanoes, are extremely 

 susceptible to weatlieriiii>', the ledges and cliffs thereabouts 

 are carved into caves, pinnacles, and manv fantastic shapes. 

 The only other rock present in any abundance is serpentine, 

 occurring in the form known as ''black marble" in a large 

 tract on the northern end of Deer Isle. This section, it is 

 interesting to note, is the most fertile in the whole area, a 

 condition directly opposed to that in most serpentine regions. 

 As will be shown later, it is the sole habitat for a few of 

 the common plants of richer soils, plants which for the most 

 part are absent from the rest of the region, since in the 

 sterile acid soils which prevail elsewhere they are unable to 

 find the necessary conditions for their existence. 



Unlike conditions in most glaciated districts the rock 

 structure still controls the topography of the Penobscot Bay 

 region, for the surface covering is very meagre and indeed 

 entirely lacking from the higher places. The soils which do 

 occur are chiefly of glacial origin, although there are a few 

 post-glacial deposits. The glacial drift or till, made up of 

 sands and gravels, is thin and irregularly distriljuted, occur- 

 ring more abundantly in the valleys. These deposits repre- 

 sent the coarser parts of the sediment which was brought 

 down by the ice and deposited on the land. The finer por- 

 tions, on the other hand, were carried on into the ocean and 

 laid down as clay. ]\Iost of the present lowlands of the region 

 have a covering of this very fine grained marine clay, but 

 above the 125 foot level and on the steeper slopes this deposit 

 is lacking. Wherever it occurs the clay is a conspicuous 

 feature of the landscape, for when dry it forms a light gTay 

 dust which covers the vegetation, and when wet it turns to a 

 very sticky mud. 



Directly following the Glacial period, during which the 



