INTRODUCTION 25 



tion of Beacon Hill and the consequent isolation of the ancient 

 pine-barren flora upon it, the post-glacial migration of some of 

 the pine-barren species, and finally the present distribution of the 

 pine-barrens — coinciding as it does so closely with the Beacon Hill 

 formation — seem incontestably to point to a geological explana- 

 tion of the origin and present distribution of the pine-barrens. 

 Such a conception of the origin of this phytogeographical region 

 entails a readjustment of our ideas as to the relative age of the 

 flora and of some related phenomena; for, if this theory is correct, 

 then the pine-barrens can no more be considered as a new or 

 pioneer vegetation, but rather as an old and climax condition, 

 ancestrally infinitely more ancient than anything in the surround- 

 ing area. 



39. Another feature of the flora of the coastal plain that seems 

 to owe its existence to the action of the glacier is the finding on 

 Long Island of Pyrola chlorantha, Caltha flabellijoUa, Linnaea 

 americana and Campanula rotundifolia. Whether there existed 

 on Long Island, at the time of the glacier's extreme southern 

 movement, any vegetation or not, is a matter that will be con- 

 sidered presently. But it is significant that these northern plants 

 should have been found on the island. They are, or were, all rare 

 on Long Island, but not so northward. 



40. The extra-territorial distribution of some of the typical 

 pine-barren plants throws some additional light on the theory that 

 the pine-barrens are a phytogeographically isolated and ancient 

 region. Particularly the finding of XerophyUum, Helonias, and 

 Oceanorus, to mention only a few, on the mountains of eastern 

 Tennessee, is of interest. These and many more were found by 

 Kearney* and more recently by Small, in geologically the most 

 ancient area in America (Archaean). The hiatus in the distribu- 

 tion of these plants between the pine-barrens and these very old 

 mountains is easily explainable by the isolation theory above 

 advocated. The fact that they are wanting or very rare in the 

 intervening territory would seem to present strong evidence of 

 the unavailableness of this intermediary area (most of it was under 

 water), during the geological changes described above, for the 

 perpetuation of the species now so far isolated. Furthermore, this 



* The pine-barren flora in the East Tennessee Mountains. Plant World I: 33-35 

 1897. See also Science II. 12: 830-842. 1900. 



