92 NEW YORK STATE MUSEUM 



scarcely to be retained in the hand, similar to its condition observed 

 in natural flows. 



The clays rest upon an uneven rock surface with an intervening 

 bed of gravel or till that was deposited by the Pleistocene ice sheet 

 before Lake Albany came into existence. 



In some places the deposit is hard bowlder clay or ground 

 moraine, but more commonly perhaps it consists of gravels and 

 sands in imperfectly sorted conditions evidently laid down in front 

 of the ice by the waters issuing from it. These morainal gravels 

 and sands thicken wherever the glacier halted for any length of 

 time in its retreat and in North Albany they rise up into a promi- 

 nent ridge which overtops the adjacent banks of clay, evidently 

 marking a rather long interruption in the general withdrawal of the 

 ice northward. The Albany gravels have been considered by some 

 geologists as later than the clays, but their relations appear to con- 

 firm rather the view here given, which is that adopted by Wood- 

 worth in the work already cited. 



Above, the clays are succeeded by a layer of sand which extends 

 to the surface. The layer was the last of the Lake Albany deposits 

 and originally formed a continuous sheet over the whole area. It 

 is now very unequally distributed as the result of erosion by the 

 winds chiefly, which have heaped it up in dunes wherever the bed 

 has not been protected by vegetation. Wind action is evidenced 

 also in the well-sorted texture of much of the sand. The general 

 run of the material is fine, some of it almost as fine as loess. In 

 fact, the sand over considerable areas bears a striking similarity to 

 some deposits of loess, except for the fact that it has an argil- 

 laceous bond instead of a calcareous one. The argillaceous sands 

 are extensively shipped from the district for foundry use. 



Conformation of the Rock Surface 



The Hudson valley, in the section covered by the stratified clays 

 and sands which mark the bed of the former Lake Albany, con- 

 sists of an outer well-opened part with smoothly contoured sides 

 of gentle slope and an inner gorge that is defined by much steeper 

 rock walls. The gorge is one to three miles wide and in the stretch 

 below Albany is bottomed well below sea level, the present river 

 flowing over glacial and alluvial deposits well above the rock 

 channel. The rocks, however, come to the surface near Albany, 

 and from Troy north the gorge is above the reach of tidewater. 



