GLACIAL AND POST-GLACIAL HISTORY 653 



sea hypothesis it also makes it necessary to explain the gaps in the 

 barrier as, in part at least, due to tidal scour — an action which may 

 have been limited (see the explanation for the absence of marine 

 fossils as due to the shallowness of the water over the sills giving 

 access to the salt water, p. 651). A barrier at the east end of Long 

 Island Sound is not necessary for the existence of Lake Hudson, but 

 an altitude of the land higher than now in that region is required by 

 the supplementary explanation attached in this article to the salt- 

 water hypothesis, and an altitude but little greater would produce a 

 lake, and thus bring the Connecticut Valley phenomena and Hudson 

 Valley phenomena under one explanation. It is not meant to imply 

 here, however, that the Hudson and Connecticut water bodies were 

 one water body. It seems certain that, if they were at an early date, 

 they became independent later. 



2. The channels through the harrier and the submerged channels 

 mside and outside the harrier. — Under the lake hypothesis the outlet 

 valley was a necessary feature, and the submerged channels are the 

 natural consequences of the drainage of the lake, subsequent erosion 

 by the Hudson, and later depression. Under the salt-water hypothesis 

 the gaps must be explained as due to tidal scour which extended to a 

 depth great enough to let the streams flow through them when eleva- 

 tion had taken place, but the completion of the channels was by the 

 erosion of the Hudson at the subsequent higher stand of the land 

 and perhaps by recent tidal scour. The lake hypothesis makes the 

 gaps and extra-morainic channels now submerged, contemporaneous, 

 in part at least, with the existence of the lake. The salt-water 

 hypothesis makes them due in part to tidal scour, and in part to 

 erosion following the uplift of the land and the consequent recession 

 of the sea. 



The channels inside the moraine in Newark Bay may be contem- 

 poraneous with the later history of the Hudson Lake. Under the 

 salt-water hypothesis they follow uplift, but may be contempora- 

 neous with deltas in the upper Hudson. The fact that the disappear- 

 ance of the Newark Bay water body followed an uphft of the land 

 of just about the amount necessary to cause this water body to dis- 

 appear favors the submergence hypothesis (see p. 657). 



