baths and is extensively barred throughout its 

 length at those depths. 



West of this second channel is another plain, 

 somewhat dissected by northeasterly trending de- 

 pressions; to the east is a broad flat-topped ridge 

 with minimum depths of between 17 and 18 fm. 

 Most of the channels on the east side of this ridge 

 trend northeastward toward the Hudson Channel. 

 North of lat. 39°50' N., all of the old shelf chan- 

 nels run eastward or northeastward toward the 

 Hudson Channel. 



The gra\el deposits near these north-south chan- 

 nels seem to have added about 5 fm. to the shelf 

 surface off the coast of northern New Jersey. When 

 compared to the surface south of Long Island this 

 buildup is shown by a greater offshore extent of 

 the 20- to 30-fm. isobaths (compare charts 0807N- 

 54 and 0808N-54 and -55). According to Schlee 

 (1964), these deposits are at least 10,000 years old 

 and were probably deposited by the ancestral Hud- 

 son River. 



The northernmost and largest of the northeast- 

 ward trending embay ments runs roughly along a 

 line between lat. 39°05' N., long. 74°04' W. and 

 lat. 39°24' N., long. 73°20' W. (chart 0807N-55). 

 It is well defined between about 20 and 25 fm. and 

 occurs immediately below the submerged gravel 

 deposit described by Schlee (1964) . It can be traced 

 for some 50 nautical miles across the shelf and ap- 

 parently connects with the 37- to 38-fm. depression 

 below Tiger Scarp (chart. 0807N-52). Southeast 

 of this largest embayment are four similar but 

 smaller embayments. All of these embayments are 

 bounded on their northwest sides by low scarps 

 and all lead into a north-northeast trending series 

 of apparent lagoons and chamiels below about 

 35 fm. To the south these embayments are defined 

 by the 24- to 26-fm. isobatjis, but they arc progres- 

 sively less well formed as the end of the Brigantine 

 Shoal Ridge is approached. 



The Hudson Channel 



The Hudson Cliannel is the best defined of the 

 old river valleys on the shelf. It was first discov- 

 ered during the 1842—14 surveys and originally 

 mapped as a series of discrete "mud holes." Dana 

 (1863) later suggested that these holes were pari 

 of a continuous valley that liad been eroded liy 

 the Hudson River. The survey of 1882 demon- 

 strated tlie continuity of the channel. 



Tlie Hudson Cliannel extends some 85 nautical 



miles across the shelf from off the entrance to New 

 York Harbor to the head of the Hudson Canyon 

 (charts 0807N-52 and -54, and 0808N-55). It is 

 very shallow at its upper end. but some 10 nautical 

 miles southeast of Sandy Hook it deepens 

 abruptly, runs about 15 nautical miles southward, 

 and then turns southeastward across the shelf. It 

 is divided into a series of basins which are floored 

 with mud and muddy sand. It becomes partially 

 lost in an elongated flood plain and delta below 

 about 40 fm., but several buried channels have been 

 traced through this area, the youngest of which 

 connects to the jaresent head of the Hudson Canyon 

 (Ewing, LePichon, and Ewing, 1963) . 



According to Ewing et al. (1963), the present 

 Hudson Channel and Delta and the upper slope 

 portion of the Hudson Canyon have all been in 

 much the same position throughout the late 

 Pleistocene. Very likely, however, the present head 

 of the canyon is only one of the latest feeder chan- 

 nels for the lower canyon. Ewing et al. (1963) 

 showed some old buried discontinuities (possibly 

 erosion surfaces) which head northeast of the pves- 

 ent canyon. Robertson (1964) suggested that the 

 Georges Bank canyons were eroded during a 

 Pliocene emergence, filled during an upper Plio- 

 cene or very early Pleistocene submergence, and 

 then re-excavated during the Pleistocene. Some of 

 the canyons which are immediately northeast of 

 the Hudson Canyon, and which have their present 

 heads below 100 fm. may be of Pliocene age and 

 have not had their heads re-excavated because the 

 Hudson drainage moved out of the area. 



Terrains Between the Hudson Channel and the 

 Block Channel 



The shelf surface south of Long Island (charts 

 0808N-53, -54, and -55) has at least three types 

 of relict terrains. Between about 15 and 35 fm. it is 

 characterized by low ridges and shallow channels 

 and appears to be a stream-dissected alluvial plain 

 modified by minor features formed during the 

 Holocene transgression. It is not covered by exten- 

 sive late Pleistocene alluvial gravels like the shelf 

 southwest of tlie Hudson Channel. 



The shelf surface above about 15 fm. is domi- 

 nated by Wisconsin glacial outwash and appears 

 as a sand plain in front of the old moraines on 

 Long Island. It has been much modified b}- early 

 Holocene stream erosion, the late Holocene marine 

 transgression, the modern surf -zone, and possibly 



BATHYMETRIC MAPS AND GEOMORPHOLOGY OF MIDDLE ATLANiTIC CONTINENTAL SHELF 



00 



