Hill: Penohsrot Plants. 301 



selective absorption and take out from the soil the necessary ele- 

 ments for their own maintenance, this till afforded a favorable 

 habitat. The coastal plain plants, however, as mentioned 

 earlier, are repelled bv basic elements and are compelled to 

 seek refuge on the most sterile soils where these elements 

 are lacking. .Snch plants wonld ol)viously have been unable 

 to cross the glacial till, and their uniform northward advance 

 must have been checked until the basic materials had been 

 removed from the soil. This might have been accomplished 

 by the sinking of the coast, but we know from geological evi- 

 dence that southern Xew England has not been under water 

 since the Glacial Period. The solution of the problem is 

 found by a study of the composite distribution of certain 

 Carolinian species which have penetrated inland from the 

 coastal region. These species extend up the river valleys 

 and on the sand plains of eastern Massachusetts to York 

 County, Maine. Aji examination of topographic maps of 

 this general area shows that these sand plains are all old out- 

 wash plains.^ 



Hills to the north danuned up the water from the melting 

 ice at the close of the Glacial Period until the pressure be- 

 came too grea:t. Then the l)arriers burst and the water 

 rushed over the surrounding country leeching out the soil as 

 successfully as though it had been under the ocean. The re- 

 sulting out-wash plains now afforded a habitat suitable for 

 the advance of the coastal plain species as far north as south- 

 ern Maine. From there on the granite rocks of the coast 

 furnished an equally silicious and sterile area on which the 

 Carolinian plants pressed forward to the Penobscot Bay 

 region. 



ISTot all authorities agree as to the origin of the various 



1. Woodworth. Some Glacial Wash — Plains of Southern New Eng- 

 land. Essex Inst. Bull. 29: 71-119 (1897). 



