298 Proceedings Port. Soc Nat. Hist. 



ever, that certain Alleglianian species occur locally in the 

 Penobscot Bay area and also in considerable abundance in 

 more northern regions. How was it possible for these ]3lants 

 of rich soils to cross the sterile areas of southern New Eng- 

 land and reach the localities to the north where they now 

 occiir 'i Fernald' has called attention to the fact that the 

 glacial till left behind at the receding of the ice was a mixed 

 soil containing all the necessary elements of plant food. The 

 Alleghanian plants would have been able to penetrate far to 

 the north of their general range by utilizing the basic ma- 

 terials of this mixed soil. Conditions of climate and the 

 influence of the ocean also favored the advance of these south- 

 ern forms so that they were able to reach to Xova Scotia 

 and C^ipe Breton. 



The original continuous distribution of these austral species 

 on the drift area has been lost. As the basic elements be- 

 came exhausted from the soil for one reason or another, this 

 southern ilora gradually became restricted to localities where 

 the underlying rock furnished a soil with the proper require- 

 ments and where climatic conditions as well were particu- 

 larly favorable. This gradual extinction of Alleghanian 

 species has been pronounced in the eastern Penobscot Bay 

 region. Originally the deciduous trees were abundant but 

 the forests were cut off by the early settlers. The consequent 

 exposure of the soil to the sun and the processes of erosion, 

 or the occurrence of fires, resulted in the destruction of the 

 layer of humus necessary for the maintenance of the rich 

 woods types. These species were perhaps able to persist 

 for a while in the now unfavorable environment but soon 

 became unable to compete successfully with the coniferous 

 types which were everywhere encroaching on them, and were 



1. Fernald. The Soil Preferences of Certain Alpine and Subalpine 

 Plants. Rhodora 9: 149-193 (1907). 



