30 NEW YORK STATE MUSEUM 



of the Iroquois-Mohawk outlet its currents lowered their bed in the 

 Lake Albany deposits pari passu with the subsidence of the lake 

 waters from the surface of the deposits to the level of lOO feet. 



There is no evidence that the waters of the Hudson valley, after 

 their subsidence to the level indicated by the eroded area at Mechan- 

 icville, rose again to a higher level. The present major topographic 

 features of the valley (the terraces and their slopes) have certainly 

 not been modified by overflowing waters since their origin. If 

 therefore a water connection existed between the Champlain arm 

 of the sea and the ocean at New York, this strait had a breadth at 

 Mechanicville not greater than approximately the space between 

 the lOO-foot contour lines on the opposite sides of the valley; that 

 is a breadth not greater than that of the present valley bottom. 



These deductions, drawn from the facts of topography, are 

 opposed to the conception of a body of marine waters filling the 

 Hudson valley to a height indicated by the river deltas and con- 

 tinuous with marine waters in the Champlain depression. 



If we suppose that the Hudson valley waters in which the sands 

 and clays were deposited were estuarine, opening into the sea at 

 New York, then that portion of the estuary included in the area 

 of the Cohoes quadrangle had become changed to a fresh-water 

 river while yet the St Lawrence basin was filled with ice. We are 

 thus led to conclude that at no time was there a continuous body 

 of marine waters connecting the St Lawrence arm of the sea with 

 the ocean at New York. 



Clays, sands and gravels on the floor of the Hudson valley. 

 The materials of the floor of the Hudson valley are varied in char- 

 acter and over considerable extents of the surface are not readily 

 resolvable into areas of distribution according to their composition 

 and origin. This complexity is due to the varied factors that have 

 determined deposition of materials and their subsequent degrada- 

 tion during the successive stages of Pleistocene history. 



The strong currents which through downcutting brought into 

 relief the clay bluffs bordering the valley floor did not sweep away 

 all the deposits laid down on the middle portion of the basin of 

 Lake Albany. In places, therefore, the soil is made up largely of 

 clays representing original lacustrine deposits. Where these clays 

 thin out or where they have been largely removed by erosion, 

 glacial till appears, often with boulders at the surface. Where the 

 erosion has gone on to the extent that the till has been removed, 

 areas of bare rocks, or rocks covered with postglacial residual 

 soils, occur. 



