490 A. Lindenkohl — Post-glacial Subsidence 



reviews the well-ascertained facts connected with this depres- 

 sion but on several points reaches quite different conclusions. 



It is the object of the following pages to review the sub- 

 ject, and at the same time to introduce much information 

 bearing upon it, which has accumulated since 1885, but has not 

 appeared in print. 



Description of the Sub-marine Hudson River Channel. — 

 The sub-marine depression, to which reference is made in the 

 preceding paragraphs, has the characteristics of a river channel 

 unmistakably impressed upon it and it is recognized as the sub- 

 marine continuation of the Hudson River channel. It is first 

 noticed at a depth of twenty fathoms, about twelve statute 

 miles southeast from Sandy Hook. Its course is nearly south 

 until abreast of and eleven miles from Long Branch, where it 

 has attained a depth of thirty fathoms in fifteen fathoms of 

 water. Thence it begins to turn to the southeast and attains 

 its greatest depth of forty-five fathoms when fifty-three miles 

 from Sandy Hook, the banks rising on both sides of the chan- 

 nel to a height of fifteen fathoms within two or three miles. 

 From here its depth begins to fall off until, at a distance of 

 ninety-one miles from the Hook, the channel almost disappears 

 with a depth of but forty-one fathoms in a surrounding bottom 

 of thirty-nine fathoms depth. But, at a distance of ninety- 

 seven miles, the channel begins to assume the character of a 

 gorge or canon, which character it maintains for a length of 

 twenty-three miles, when it vanishes on the edge of the great 

 continental plateau at a depth of about 200 fathoms. The 

 average width of the river channel is about 1J miles, that of 

 the gorge three miles with a greatest depth of 474 fathoms in 

 about seventy fathoms of water. 



The bottom of the river channel and canon as well as their 

 slopes consist of a bluish slate-colored mud or clay with a fine 

 sandy grit. This mud bottom extends for a considerable dis- 

 tance on both sides, north and south of the canon along the 

 brink of the continental plateau. 



In trying to account for the existence of the upper part, or 

 river portion, of the channel, it was assumed to be the result 

 of fluvial erosion and to imply a subsidence of about 210 feet 

 at a comparatively recent geological time, subsequent to the 

 glacial period. The existence of the gorge was believed to 

 imply a much greater subsidence than that of the upper chan- 

 nel, a subsidence not far from 1200 feet (200 fathoms). No 

 attempt was made to fix its geological date beyond the state- 

 ment that its fiord-like shape favors the supposition that it 

 existed as an elevated channel during a part at least of the 

 glacial era, but that it must have sunken below the level of the 



