600 H. L. FAIRCHILD POST-GLACIAL UPLIFT OF NEW ENGLAND 



(1) Under the conception of open water laving the waning glacier 

 and too deep for effective wave-work, the theoretic succession and char- 

 acters of the deposits wonld be somewhat as follows : The foundation for 

 the water-laid deposits might be either rock or till. The till might be 

 differentiated, but if the marginal ice were thin and not too heavily 

 loaded with drift, it might be floated away, leaving only the subglacial 

 till, or perhaps none at all. The massive clay in the Hudson Valley 

 often rests on glaciated rock. In the lake area of southeastern Massa- 

 chusetts it appears that detached ice blocks were anchored and more or 

 less buried in sand and gravel, producing a multitude of kettles. 



The earliest (lowest) water-laid deposit from the glacial outwash 

 would vary from cobble to sand and would commonly include much 

 coarse material. 'If the detritus were poured into deep water, it would 

 receive little assorting and would produce unstratified or pell-mell 

 structure. The finer suspended matter would generally be swept away, 

 leaving the deposits without silt, although in sheltered localities some silt 

 might rarely be added to the primary deposit. As the ice-front receded 

 the suspended silt would be floated out and precipitated over the earlier, 

 coarse, pell-mell deposits. Locally, in case of very vigorous stream 

 outwash, effective current might carry sand some distance seaward and 

 spread it with partial stratification; but streams from the glacier into 

 deep, wide water would commonly be too quickly checked to produce 

 stratification. 



When the ice-front was far removed, only the finest, suspended silt 

 could reach the deserted area, and the coarse, pell-mell deposits might 

 receive a topping of clay. 



Out of the possible variation in the deep-water deposits there remains 

 the broad fact of coarse detritus at the base with prevailing pell-mell 

 structure, and silt at the surface over the greater area of submergence. 



It appears that the rise of land was nil during the removal of the ice- 

 sheet from the area, or at least so small in the coastal region as to be 

 negligible. 



The next phase in the theoretic history involves the rise of the un- 

 weighted land and the shallowing of the waters, implying seaward exten- 

 sion of the dry land and lengthening of the rivers. The clays from the 

 glacial drainage might shade into the silts and clay from the subsequent 

 river contribution. Within the range of river currents the clays might 

 eventually suffer erosion, by river work or tidal scour, and over the ir- 

 regular surface sand or gravel might finally be spread, as the latest work 

 of the shallowing waters. Sharp unconformity between clav beneath 



