432 Dana — Submarine Hudson River Channel. 



Island and Montauk Point stretch out under water far toward 

 one another, and therefore the deepening (see map) from 12 

 fathoms to 27 and 30 over the narrow interval is a reasonable 

 result for scour. The loops farther south in the bathymetric 

 lines are too broad to be relied on for any conclusion. The 

 channel between Montauk Point and Block Island must have 

 been the course of the northern of the two water-ways of the 

 Sound, if Long Island stood 100 feet or more above its present 

 level in the Glacial period ; but tidal scour accounts well 

 for the present condition of the region. 



2. The Hudson River Channel. — The method of explana- 

 tion above suggested for the supposed Connecticut Piver Channel 

 does not meet the case of the supposed Hudson Piver Channel. 

 But still it may be that tidal scour has had much to do with 

 the present shape also of the latter channel, [t may be that 

 the outflowing tide from ISTew York Bay and from the adjoin- 

 ing parts of the shores of Long Island and ISTew Jersey may 

 have combined their forces along a diagonal line crossing the 

 shallow Atlantic border region, and, by scour only, have given 

 the existing depth as well as course to the larger part of the 

 channel. The water, on the ebb, from this inner portion of 

 what Professor Bache named in 1858 the Middle Bay of the 

 American Coast (between Cape Hatteras and Nantucket) move 

 or settle away on more or less oblique courses toward the 

 lowest part of the bottom for escape, and there they flow most 

 rapidly and would erode most energetically. 



Effects of inflowing tidal and wind-made currents on depo- 

 sitions. — To appreciate the effect of the ebb on the channel, 

 the work carried on by the inflowing tidal wave and wind- 

 made currents should be in mind. The wave, moving toward 

 New York, the head of the great Middle Bay, gives the sands 

 which the waters take up from the coast and in the shallow 

 waters a corresponding drift or set along the beaches. This 

 drift action on the New Jersey coast is carried on, as was long 

 since shown by Professor Bache, to the extremity of Sandy 

 Hook, at the very entrance to New York Bay ; and on the 

 Long Island coast in like manner, as abundantly illustrated by 

 Lieutenant (later Admiral) C. H. Davis, U. S. N.,* it works 

 even to Coney Island, by the north side of the entrance. The 

 course of tidal action in and out, producing the western set of 

 the sands and other materials at the inflow, is well shown by 

 the oblique loops in the bathymetric lines of 10 fathoms, south 

 of western Long Island. Wind-made currents, due to the 

 prevalent eastern storms, work in the same direction, perform- 

 ing much of the transportation. 



* Geological action of the tidal and other currents of the Ocean, by C. H. Davis, 

 A.M., Lieut. U. S. N., Mem. Acad. Arts and ScL, new series, iv, 1849. 



