190 



EDGAR NELSON TRANSEAU 



habitats. The absence of streams from a large part of the island 

 is a natural consequence of the underlying sand and gravel. 



The oldest rocks are of Cretaceous age, and these form the basis 

 of all the major topographic features of the island. The present 

 topography was developed in late Pliocene. According to Veatch^ 

 the area was invaded five times by glaciers. The last two invasions 

 were phases of the Wisconsin epoch, and to them we owe the kettle 

 holes of the morainic portion and the extensive outwash plains. 

 There may have been vegetation on the southern margin of the 

 island during these latter cold epochs but it could hardly have 

 contained any of the present coastal plain plants. 



Fig. 1. Sketch Map of Long Island showing relation to the mainland, position 

 of the ternainal moraines, and the larger divisions of the vegetation. Compiled 

 from data furnished by Mr. Henry Hicks, Dr. H. N. Whitford, U. S. Geological 

 Survey maps. Bowman's Forest Physiography, and personal observations. 



Since the retreat of the glaciers the most important changes 

 have been the building of spits and bars, the erosion of the head- 

 lands, and the development of marshes inside the harbors. Dur- 

 ing the postglacial period the altitude of the land probably varied 

 somewhat with reference to sea level. Hollick^ has accounted for 

 the occurrence of pine barren plants on Long Island and the islands 



' Veatch, A. C. Underground Water Resources of Long Island, New York . 

 Professional Paper No. 44, U. S. Geol. Surv. 1906. 



2 HoUick, Arthur. Plant Distribution as a Factor in the Interpretation of Geo- 

 logic Phenomena. Trans. N. Y. Acad. Sci. 12: 189-202. 1893. 



