FLORA OF VICINITY OF NEW YORE 550 



of tlie flora existing at that time. It is obvious that whatever the 

 effects of geological eras before the ice age may have been on the then 

 existing flora, this great ice sheet must have obliterated all the vegeta- 

 tion in the region which it covered. All the region north of the south- 

 em edge of the continental ice sheet must have started with vegeta- 

 tively a clean slate, as it were, when the ice receded. What was the edge 

 of the ice sheet is now marked by an irregular range of hills which 

 stretch from Montauk Point to northeastern Pennsylvania. These 

 morainal hills mark the present southerly distribution of many of our 

 species of plants. Over 8 per cent, of our native flora has never been 

 found south of these morainal hills, notably the red pine {Pinus resi- 

 nosa), the balsam (Ahies balsamea), yellow birch (Betula lutea) and 

 Quercus lorealis among the trees; Rihes glanduhsum, the shrubby 

 cinquefoil {Dasiphora fruticosa), many thorns, the RJiodora and Kal- 

 mia glauca among the shrubs, besides scores of herbaceous plants. 



This glaciated part of the range is characterized, too, by the large 

 percentage of hardwood deciduous trees, and by the great number of 

 introduced plants that are found there. Most of our European weeds 

 flourish in the much-cultivated region north of the moraine. 



The unglaciated part of the area is mostly occupied by the coastal 

 plain which, on the whole, is characterized by the long sandy or gravelly 

 stretches that are found on southern Long Island and New Jersey. 

 All of the region is geologically the most recent in the area, the surface 

 being largely made up of Tertiary and Cretaceous deposits in New 

 Jersey and over-wash material from the glacier on Long Island. From 

 the standpoint of the botanist the chief thing of interest about the 

 coastal plain is the pine-barren region of New Jersey. This region is 

 so unusual that the ordinary traveler is at once struck with the differ- 

 ence between these sandy stretches of pine-tree vegetation and the 

 richer flora further north. 



It has been shown^ that the pine-barrens occupy almost exclusively 

 the Beacon Hill formation, in New Jersey, w'hich has been uninter- 

 ruptedly out of the water since upper Miocene time, and has been sev- 

 eral times partly, or wholly, surrounded by sea water. Because of its 

 continual emergence it is the oldest region in our area that can have 

 been continuously covered with vegetation. For the region surround- 

 ing the barrens was subject several times to the invasion of sea water, 

 and as we have seen the glaciated area, geologically much more ancient, 

 must have been fairly scraped clear of vegetation by the ice. In other 

 words, the New Jersey pine-barrens exist exclusively on the Beacon 

 Hill formation, an area isolated by geological processes and maintain- 

 ing a relict flora, which is much older in permanency of occupation 

 than any of the rest of the flora near New York. 



Ancestrally our local flora must have consisted of purely American 



2 Torreya, 12, 229-242, 1912. 



