THE GEOLOGY OF LONG ISLAND, ETC. 



of interest indicating the nature of the process, i. e., marsh 

 formation during recent years are those of Johnson, York, 

 and Conard, loc. cit. Harshberger ('07-'16) has also made 

 marked contributions to our knowledge of the vegetation of 

 these salt marshes. 



The bluffs of the open northern coast are mostly free from 

 vegetable growth. The remainder are artificially covered 

 with grasses, trees and other vegetation as at Cooper's Bluff. 

 The whole line of the coast may be changed by a single 

 storm which may eat into the bluffs, or throw up in front 

 barriers of sand gravel according to the direction of the 

 wind, angle of impact of the waves and nature of the cur- 

 rents set up. As the larger stones that slide dov/n the bluff 

 are moved but little if at all by the waves, they accumulate 

 in some places and there protect the shore. The barriers 

 stay until removed by storms and currents in other direc- 

 tions. Some last for years on account of grasses and trees 

 taking possession of them, but sooner or later cutting be- 

 gins again. The cliffs are best preserved where coherent 

 materials exist in them. Good exposures of their component 

 structures are found at Eaton and Lloyd necks. In the reg- 

 ions where they are destroyed there ensue lesser bars, 

 beaches and spits connecting smaller islets with the main- 

 land or projecting into harbors, (such as the sand spit at 

 Cold Spring Harbor) , the bays or the sound. Generally, 

 the current flowing out of the inlet is strong enough to keep 

 a narrow channel open, but the waves form a hook at the 

 tip of the spit. The prevailing direction of the wind on the 

 north shore is westerly, but the direction changes frequently, 

 when under certain conditions spits may be extended from 

 both sides of a point or inlet. Such processes have largely 

 made the shore of Long Island more regular. A detailed 

 account of the formation of the sandspit at Cold Spring 

 Harbor and its animal ecology has been given by Daven- 

 port, ('03), while the plant ecology has been studied by 

 Johnson, York and Conard (loc. cit.) 



Long Island thus appears to have been the result of the 

 opposed agencies of deposition and erosion. It is compara- 

 tively small now, for since Cretaceous times erosion has pre- 

 dominated over deposition. It is estimated that the amount 



—15— 



