THE GEOLOGY OF LONG ISLAND, ETC. 



sand may compose all or nearly all of it. The sandy phases 

 are developed chiefly at the eastern end, the clayey phases 

 at the western end of the island. Boulders, large and small 

 are scattered freely upon the surface and throughout the 

 mass of both moraines. They are of variable composition — 

 gneiss, schists, sandstones and quartzites predominating. 



The long, gently sloping out wash plains extending south- 

 ward from the moraines have been mentioned. Their north- 

 ern margins are in many places pitted by kettle holes. Ex- 

 amples of these kettle plains are found west of Cold Spring 

 Harbor station at Syosset and southwest of Huntington at 

 the fair grounds. Where kettle holes have permanently 

 obtained a water supply they have frequently influenced the 

 settlement of the island. Two papers by Conard ('13-'23) 

 deal with the revegetation of an area near Syosset which 

 had become denuded artificially, and his observations yield 

 clues as to the method of the first occupation of these out- 

 wash plains by the post glacial .flora of Long Island. 



The porous nature of the outwash material greatly re- 

 duces the run off of precipitation and instead of a normal 

 run off of about 30%, such is only about 20% of the normal. 

 The reduced run off has retarded the dissection of the 

 frontal plains and the small elevation has favored the same 

 result. There extend mile after mile of almost flat plains 

 of alluvium in striking contrast to the ruggedness and pic- 

 turesqueness of the terminal moraine. Plenty of old chan- 

 nels mark the beds of former streams, but few streams flow 

 in them. The present drainage consists chiefly of small, 

 wet weather streams extremely diminutive as compared 

 with the ancestral streams whose channels they occupy. 

 Veatch ('06) has shown that the effect of dams on the 

 brooks of Long Island is to very materially decrease the 

 stream flow at the points where dams are erected, and keep- 

 ing in mind the foregoing, it may be deduced that a large 

 amount of water escapes through the porous sides of the 

 pond. Illustrative of the effect of this condition on vegeta- 

 tion of Long Island is Harper's account of a Long Island 

 cedar swamp ('07). This swamp is located at Merrick, near 

 the south shore of the island. 



Excavations on the plain expose waterworn gravel and 



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