602 H. L. FAIRCHILD POST-GLACIAL UPLIFT OF XEW ENGLAND 



setts these plains of erosion have been wrongly attributed to glacial lako 

 waters. 



Without long pauses in the land uplifting, or a stand-still of the 

 waters, erosion features such as sea-cliifs, or constructional features such 

 as spits and bars, would not be formed (TT, page 299 : 81, page 199). 



{2} Under the conception of shallow waters laving the receding ice- 

 front, so shallow that stream-flow and offshore currents were effective, 

 the unassorted or pell-mell gravels that are characteristic of deep-water 

 genesis would be absent and would be represented by plains of stratified 

 materials sloping seaward. Such submarine plains should exliibit very 

 smooth surfaces, and the materials should grade, horizontally, from 

 coarse to fine as the offshore depth increased. In line with the entrance 

 of streams of glacial outwash, shallow scourways would exist, and as they 

 concentrated the tidal ebb and scour, they might persist and extend sea- 

 ward, as* the land rose, perhaps even without the aid of stream currents. 

 The smooth plains of Long Island, Marthas Vineyard, and Xantucket 

 are considered good examples of submarine plains in shallow water. 



The final rise of the land would leave the surfaces that had fallen 

 within the range of detritus with deposits more or less differentiated, 

 as noted above. Pell-mell structures and smoothed kame areas would 

 be wanting. AMien land streams came into existence their work would 

 be mostly erosional in the belt of the shallow-water deposits. In this 

 connection it becomes important to discriminate the constructional, o? 

 outwash. plains from the erosional, or wave-leveled, plains (see page 609). 



(3) Detrital plains built above the sea, or other standing water, oi 

 subaerial construction should possess some characters that would distin- 

 guish them from subaqueous plains. Such discriminative characters 

 have not been recognized, for the plains of Long Island and Xantucket 

 have been referred to both classes of deposits. Geologists who deny 

 the recent submergence of the coastal region regard these plains as 

 subaerial glacial outwash. The very level surfaces are supposed to be 

 produced by the blending of alluvial cones by lateral migration of loaded 

 streams, or as the aggraded upper, subaerial portions of vast united 

 deltas. A brief discussion of these plains may suggest some criteria. 



The plains lack the anastomosing channels of "braided"^ rivers on 

 aggrading deltas, and the dividing or distributary channels of either 

 fans or deltas. On the contrary, the ^^creases,'^ or so-called channels, 

 unite seaward, widening and becoming undefined. They do not hold 

 coarse detritus, as rounded boulders and cobble, which should be the 

 case if formed by land streams, but, especially on the lower ground, are 



