26 NEW YORK STATE MUSEUM 



These deposits are interpreted as a valleyward extension of the 

 deka and as representing that portion of the deha which was built 

 up above the level of the general delta platform of the lake. This 

 principle of delta growth has been stated as follows : "At the 

 same time the channel of the stream above the original head of the 

 delta is aggraded, for the current there is checked by the aggrada- 

 tion of the delta. Thus alluvial deposits continuous with the delta 

 are extended landward.''^ 



DEVELOPMENT OF THE HOO-SIC TERRACES 

 The river had built into Lake Albany a great delta, the plain 

 of which had been raised above the level of the water at the head 

 of the delta, near Schaghticoke, and stood very shghtly below the 

 water level for a considerable distance outward from the head. 

 When at length Lake Albany began to subside this portion of the 

 delta plain, covered by shallow water, emerged as land surface. 

 During the emergence the river maintained its channel across the 

 added area but as the extent of the level or slightly sloping surface. 

 increased, the stream was gradually thrown into a winding course 

 and eventually broad meanders were developed. The continued 

 degradation of the bed of the river resulted in lowering the level 

 of the plain within the belt of meandering. Li the shifting of the 

 channel of the stream from side to side terraces were left at the 

 outer limit of each meander. These terraces were formed at suc- 

 cessively lower levels according to the level of the lowering plain 

 at each successive swing of the river. 



The subsidence of Lake Albany by stages, bringing to the sur- 

 face at different times added areas of the delta surface, was 

 undoubtedly an important factor in the development of the terraces. 

 It is possible that the slopes bounding some of the terraces repre- 

 sent in fact abandoned shore lines of the lake. The terrace on the 

 north side of the river at the 280-foot level at its inner margin and 

 bounded at its outer margin by the slope that separates it from the 

 340-foot level of the delta plain lends itself to this explanation. The 

 contour lines that mark the 20 feet of slope trend abruptly to the 

 northeast and can scarcely be interpreted as indicating the limit of 

 a meander. The writer has not found it possible, however, on the 

 basis of topographic evidence, to differentiate between the effects 

 to be immediately connected with subsidence and those due to 

 erosion and meandering as described above. 



^ Chamberlin and Salisbury. Geology, i:ii 



