ANCIENT WATER LEVELS OF CH A MPLAIN— HUDSON VALLEYS 73 



more accurate index of the elevation of the coast in recent times 

 than the measured depth of a channel whose origin is subject to 

 some doubt. 



The most important light from the immediate vicinity of the 

 mouth of the Hudson concerning high elevation has been presented 

 by Yeatch 1 on the basis of borings made in the glacial deposits of 

 Long Island. An elevation of at least 250 feet is indicated pre- 

 vious to the deposition of the Jameco gravels, beds seemingly near 

 the base of the Pleistocene series, but separated from that base on 

 Long Island by deposits tentatively correlated with Professor 

 Salisbury's Pensauken group by Yeatch. The whole history is 

 one of alternating elevation and depression above and below the 

 present stand of the sea in relation to the land. 



As is frequently repeated in the later pages of this report, the 

 submarine Hudson channel makes it possible to admit high eleva- 

 tion whenever the fads over the land on the north require such an 

 interpretation of its history. 



The Hudson gorge from New York city northward is fairly dis- 

 tinct, as far as the vicinity of Fort Edward, where it widens out 

 into the Fort Edward basinlike district; yet over the floor of this 

 basin a shallow but definite rock trench is traceable northeast- 

 ward along the course of Wood creek to the head of Lake Cham- 

 plain. 



Hudson rock terraces. The excavation of the gorge below the 

 floor of the ancient Hudson valley has left well defined rock ter- 

 races bordering the Hudson. The terraces and the gorge have 

 alike been somewhat modified by glacial action, glacial striae 

 being observed very generally along the river banks through the 

 whole length of the valley except in such places as recent rock 

 falls from the steep bank have exposed new sections of the bed 

 rock. 



The elevation of these terraces must correspond approximately 

 therefore with the lower levels of the ancient valley floor of the 

 Hudson. The following figures represent the present attitude of 

 the rock terraces between New York city and Fort Edward. 



'Yeatch, A. C. Diversity of the Glacial Period on Long Island. Jour. 

 Geol. 1903. 11:702-76. 



