62»1 NKW YOKK STATE MUSEUM 



pebbles, which l>ecoines converted into a liard stone layer, the inside 

 reiniiinin^ usually unconsolidated. When in after time these 

 ncKlules are wrested from the bed in which they originate, they are 

 bn»ken o|Xjn, the clayey or sometimes sandy interior washes out and 

 there is left a |>otlike, hollow jwbble of the kind known as aetites or 

 eaglestone.' Hundreds of these nodules were dragged out of their 

 bedding places by the advance of the ice over the Columbia at the 

 time of makiuir the terminal moraine on Marthas Vineyard and in 

 portions of Ix)ng Island. 



The occurrence of these nodules at the locality mentioned affords 

 evidence that the underlying white clays and sandy cla}8 were 

 eroded at the beginning of Columbia deposition. The uncon- 

 formity thus inferred is widespread to the east on Marthas Vine- 

 yard and Block island and along the Atlantic coast southward to 

 the vicinity of Washington. Of direct local evidence, little can be 

 said. On the shore north of Coldspring the gravelly beds at the 

 base of the tilted Pleistocene series may be seen resting on the 

 Cretaceous and older clavs, but there is no observed difference of 

 dip, though the absence of identifiable Eocene or Keocene beds is 

 pnxjf of an unconformity. No clearer fact than this was gathered 

 from the similar sections about Glen Cove and Glenwood. 



Aside from this unmistakable instance of older gravels lying out- 

 side of the moraine, it is uncertain to what extent the older beds make 

 up the frontal plain. Yellowish gravels abound in the road and 

 railroad cuts, but the yellow quartz pebbles have invariably l>een 

 wa.shed and worn since they were stained, and similar pebbles are 

 now working their way from the cliffs down the beach slopes into 

 the dejxjsits now making along the coast. It is to be inferred, how- 

 ever, from the attitude and thickness of the Columbia north of the 

 moraine that a large ])art of the section south of the moraine is 

 composed of these beds. 



The structure of these beds is revealed in only a few pits and 

 coastal sections. The most extensive exposures in 1900 were found 

 in a numl)er of sand pits on the west shore of Hempstead harbor. 

 In these pits the beds are horizontal, and the boulder clay bed is 

 clearlv traceable. 



'Geikie. A. Textbook of geology. 3(1 etl. 1893. p. 14^-47 



