LONG ISLAND VEGETATION 



191 



to the eastward on the assumption that the land stood from 100 

 to 200 feet higher than at present, thus forming an almost contin- 

 uous land surface from New Jersey to Cap Cod. Veatch doubts 

 Hollick's conclusion and fails to find any corroborative evidence 

 from the geological record. ^Moreover Salisbury'' gives evidence 

 that the land along the New Jersey coast has risen relative to the 

 sea some 50 or 60 feet in postglacial times. On the basis of the 

 tilting of the glacial Lake Passaic beaches, it is to be presumed 

 that the Long Island coast has risen even more. On the south 

 shore there is undoubted evidence of recent sinking, but this is too 

 insignificant to be of importance in the matter of plant migration 

 to the island. 



The validity of Hollick's conclusion, that a former land connec- 

 tion is required to account for the presence of coastal plain plants 

 on Long Island, depends not so much upon the fact that a number 

 of these species are found there as upon the proportion of these 

 plants found in northern New Jersey that cross the New York 

 harbor barrier. The magnitude of this barrier can only be esti- 

 mated by comparing its effects with the effects of other water 

 barriers along the coast. 



To this end I prepared a list of the species practically confined 

 to the coastal plain, and whose southern limit is south of Virginia. 

 This excludes from the list of Long Island coastal plain plants 

 only eleven species which are either endemic or do not extend so 

 far south. The list includes 298 species. Assuming that the 

 present northern limit of these species is determined largely by 

 physiographic factors, the important barriers to the northward 

 migration of these species are Chesapeake Bay, Delaware Bay, 

 New York Harbor, and the termination of the costal plain in east- 

 ern Massachusetts. If New Jersey stood lower in early post- 

 glacial times there would also be a water barrier in the central part 

 of that state. Of course climatic factors are involved in limiting 

 the northward range of these plants. For example the excess of 

 rainfall over evaporation shows a marked decrease northward. 

 There is also a decrease in the absolute minimum temperature 



' Salisbury, R. D. Glacial Geology of New Jersey. N. J. Geol. Surv. 1902. 



