592 NEW YORK STATE MUSEUM 



of the material washed into the estuary. During the period of 

 submergence much of the silicious matter washed into the estuary 

 was deposited at the mouths of the tributary streams to form deltas. 



It has been suggested by Dr MerrilP that the change in the 

 estuary deposits from clay to sand might be due to the exposure 

 by elevation of an area of land around the basin, which would 

 afford more silicious matter. 



An elevation would be accompanied by an acceleration of the 

 streams, and much of the silicious matter transported by them 

 would be carried farther out into the estuary and spread over its 

 bottom, while the finer clayey sediment would be carried out to 

 sea. A readvance of the ice, it would seem, would likewise cause 

 an acceleration of the streams, and with the results stated above. 



To account for the isolated boulders in the clay, it seems highly 

 probable that icebergs or icefloes having stones and dirt imprisoned 

 within their mass detached themselves from the retreating glacier, 

 and, floating down the estuary to the sea, dropped their burdens. 



The unstratified material found with it and in some cases over- 

 lying the stratified delta deposits is a matter of interest as con- 

 cerns its origin. Three things may be noticed regarding it. 



1 The material is sand, pebbles and cobblestones lying mixed 

 together without any separation of the coarse from the fine.^ 



2 The pebbles and stone are rounded and do not show any 

 scratches. 



3 The materials are mostly of the same character as the rocks of 

 the vicinity. 



ISTow as the land rose from its submergence the velocity and 

 with it the transporting power of the streams would increase, 

 washing down quantities of large stones and gravel. Dr Merrill 

 considers that a rapid fiow of water took place down through the 

 Hudson valley in the late Quaternary. This water must have come 



1 Amer. jour. sci. June 1891. 



^ The only locality where stratification was observable was at Timoney'a 

 yard, near Dutchess Junction. 



