Dana — Submarine Hudson River Channel. 4.33 



For this drift movement on the Long Island coast, sands are 

 contributed by the high gravel-made bluffs of the seacoast to 

 the eastward, toward Montauk Point, and thus the supply of 

 new material on the Long Island side is larger than on the 

 New Jersey side, notwithstanding the aid in deposition the 

 latter has from rivers. Accordingly, the work has not only 

 made the long lines of beaches off the Long Island shores up 

 to the New York entrance outside of a series of long bays or 

 sounds, but has probably widened the shallow region off the 

 western part of Long Island, that is, the area under 15 fathoms 

 in depth. If so, these drifted sands have been the means of 

 giving the so-called Hudson River channel a shove far toward 

 the New Jersey shore, and also the bend in it just south. In 

 the ebb, the waters from the coast of Long Island and New 

 Jersey would carry down shore sands and drop them over the 

 bottom on the way to the channel. The origin of the blue 

 clay or mud of the bottom of the channel, to. which Mr. Lin- 

 denkohl draws attention, is not certain. Recent borings on 

 the New Jersey coast at Atlantic City (lat. 39° 20' N.) reported 

 by L. Wool man, reached a depth of 1400 feet without getting 

 below Miocene.* Clay and marl beds occur at intervals, which 

 are nearly continuous below 383 feet. 



Description of the channel. — Turning now to the channel, 

 the conditions are found to be, in part, at least, legitimate 

 effects of scour. 



The channel may be traced up to the mouth of the "East 

 Channel," the central one of the channels intersecting the sand 

 bars at the mouth of New York harbor. The soundings, 4J, 

 7, 8J, 9 fathoms, lead down from it to the 10-fathom area 

 marked on the map ; and this incij>ient trough has a depth of 

 1 to 1^ fathoms below the surfaces adjoining.f The water 

 through the Swash and the Main Channels (the two southern) 

 pass into the trough or channel over its side instead of by a 

 separate branch channel ; and this fact suggests a reason for 

 the channel's leading off from the central East Channel instead 

 of the deeper Main Channel : it is more remote from the New 

 Jersey coast near by, as well as from the Long Island coast, 

 whence sands drift to the sand-bars with the inflowing tide. 



The pitch in the trough or channel from 5 fathoms to the 

 10-fathom line, a distance of one and two-thirds mile (statute), 

 has the mean rate of 18 feet a mile ; from the same to a depth 

 of 15 fathoms, about 5 miles distant, 12 feet a mile ; to a depth 

 of 20 fathoms, 10 miles distant, 9 feet a mile. The bottom of 

 the channel has thus a continuous but lessening pitch from the 



*Proc. Acad. Nat. Sci. Philad., March 25, 1890. 



f These soundings are given on the Coast Survey Chart of New York Bay, (No. 

 120). They were inserted on the map for the plate accompanying this paper, but 

 are obscurely copied. 



