GLACIAL AND POST-GLACIAL HISTORY 651 



have been abundant opportunity for life to come into the Hudson 

 , over the low land between Long Island Sound and the Hudson, and 

 the Connecticut Valley deposits, which appear to resemble those of 

 the Hudson in many respects would be expected to show abundant 

 marine life. 



It may be said, however, that this argument of shallow water over 

 the sills has its limitations. It has been shown that it is necessary to 

 believe that the channels through the moraine were cut down a con- 

 siderable amount before the Hudson water body disappeared. On 

 the submergence hypothesis tidal scour must be relied on to do this 

 cutting, and reduction of the amount of water to get in over the sills 

 at high tide reduces the amount that could go out with the ebb, and 

 thereby proportionally reduces the efhciency of scour; and if none 

 comes in, the scouring is reduced to the action of the fresh water 

 supplied by the streams. This limitation would be more severe in 

 Newark Bay perhaps than in the Hudson, where the great amount 

 of fresh water flowing from Lake Iroquois into the Hudson waters 

 after the Rome outlet came into use would be available for scouring 

 the channel. The argument would not apply so well, however, in 

 explanation of the absence of marine life in the Connecticut Valley. 

 The demands of later events require a scouring out of the Hudson 

 channel at the narrows to a considerable depth — possibly as much 

 as 122 feet — before the Hudson water body disappeared. It would 

 seem that this amount of scour would admit plenty of salt water and 

 marine life. It may be, however, that water in the scoured channel 

 was kept shallow by uplift, and the supply of salt water was thereby 

 limited. Altogether it would seem possible that the explanation 

 offered might account for the absence of marine life in the Hudson, if 

 the dehcate adjustment required to keep the water shallow over 

 the sills existed. It is not known, however, that the conditions postu- 

 lated actually did exist. The explanation would not apply to the 

 phenomena in Long Island Sound, and in the Connecticut Valley, if 

 the altitude of the land was as low as at present. It is doubtful if it 

 is adequate even for the Hudson Valley phenomena without a higher 

 altitude of land at the east end of Long Island Sound. This higher 

 altitude is a requirement of the same kind, and nearly as great, as for 

 the lake hypothesis in both the Hudson and Connecticut Valleys, and 



