Broecker (1966), are: (1) a maximum Illinoian 

 lowering of about 75 or 88 fm. (some 110,000 years 

 ago), (2) a maximum early Wisconsin lowering 

 of about 63 or 74 fm. (some 53,000-60,000 years 

 ago), and (3) a maximum late Wisconsin lowering 

 of about 58 or 68 fm. (some 18,000-20,000 years 

 ago). 



In addition to these three terraces, Garrison and 

 McMaster (1966) have noted the existence of an- 

 other terrace formed when sea level stood at about 

 45 fm. This level seems to have been the latest 

 episode in (1) large delta formation, especially 

 south of New England, and (2) extensive barrier 

 beach-lagoon formation off New Jersey and Dela- 

 ware. The 45-fm. terrace is well developed near 

 the Block Delta, where there is also evidence of 

 small lagoons to the east (chart 0808N-52) , and of 

 a large spit and a barrier beach-lagoon complex to 

 the west (charts 0807N-51 and 0808N-54). The 

 terrace is also well developed between the Block 

 Delta and the Hudson Canyon (chart 0807N-52) 

 and between Toms and Wilmington Canyons 

 where a large embayment and an extensive series 

 of barrier beaches and lagoons seem to have formed 

 (chart 0807N-53). 



Delfa.s. — Old river deltas along the 45-fm. ter- 

 race are especially well developed northeast of the 

 Hudson Channel. The 45-fm. level was the most 

 recent ejjisode in a long history of large-scale del- 

 taic deposition on this part of the outer shelf. The 

 most typical and best preserved of the old deltas is 

 associated with Block Chamiel (Garrison and Mc- 

 Master, 1966). From seismic profiles Krause 

 (1966) has concluded that this delta probably- 

 existed throughout the Pleistocene. Where it bulges 

 out over the edge of the shelf and onto the upper 

 Continental Slope, Krause's profiles revealed a 

 large area of bottomset beds. 



Between the Block and Hudson Deltas a small 

 delta is associated with the southeasterly drainage 

 pattern south of Long Island. Probably of late 

 Wisconsin or Holocene age, this delta appeare to 

 lie almost completely above the 64-fm. terrace 

 northeast of the Hudson Canyon (chart 0807N- 

 52). 



The Hudson Channel disappears below about 40 

 fm. in what Veatch and Smith (1939) have called 

 the Hudson Apron, a large delta whose latest 

 stage of construction occurred when sea level stood 

 at about 43 fm. The large bar, or spit, just to the 



northeast of the Hudson Canyon, may represent 

 the remains of an earlier delta built during or 

 shortly after the late Wisconsin maximum sea level 

 regression (which probably formed the 64-fm. sur- 

 face under this feature) . Similar large spits to the 

 northeast of both Wilmington and Baltimore Can- 

 yons (chart 0807N-56) may also be remnants of 

 early or late Wisconsin deltas — probably built in 

 this area by the Delaware River. Little evidence 

 exists of delta formation at the 45-fm. level east 

 of Block Chamiel. 



Canyons and the. slope complex. — The Continen- 

 tal Slope of Eastern North America was discov- 

 ered in the early 19th century, but it was not 

 studied in detail until the 1870's, when the first 

 successful wire-sounding machines were intro- 

 duced. The Coast Survey steamer Blake surveyed 

 the slope during 1877-80 (Agassiz, 1888), and the 

 Fish Commission steamers FhJi Hawk and Alha- 

 fross did extensive deep-water biological dredging, 

 especially south of New England, during the 

 1880's. 



Although the upper parts of canyons on the edge 

 of the Scotian Shelf and Grand Banks had long 

 l)cen known to connnercial fishermen (see Collins, 

 1885, and Johnson, 1885), no evidence of Middle 

 Atlantic canyons was obtained until the 1842 work 

 of the Coast Survey. After the soundings from the 

 1842 surveys were plotted, nautical charts carried 

 notations of a "145-fathom hole" near the head of 

 Hudson Canyon. Dana (1863) used an 1852 chart 

 to trace the Hudson and Block Channels across 

 the Shelf, but the new surveys of 1882 were re- 

 quired to show the immense size of the Hudson 

 Canyon and its extension to the bottom of the 

 Continental Slope (Lindenkohl, 1885). The upper 

 part of another canyon, later named the Atlantis 

 Canyon, was discovered by the Albatross in 1884 

 (Tanner, 1886) . After the discoveries of the 1880's 

 the canyons were much discussed (see Upham 

 1890a, 1890b, 1894: and Spencer, 1890, 1903, 1905a, 

 1905b) — usually in attempts to support theories 

 of a vast uplift of the North American continent 

 during the late Tertiary or early Pleistocene, which 

 was supposed to have caused the ice age — but little 

 new field work was done until the surveys by the 

 T'SCGS in the 193()"s (discussed by Shepard, 1931, 

 1933a, 19.33b, 1934, 1938; Daly, 1936; Shepard and 

 Beard, 1938 ; and Stetson, 1938a, 1938c) . This work 

 culminated in the report and cliai'ts of Veatch and 



BATHYMETRIC MAPS AND GEOMORPHOLOGY OF MIDDLE ATLANfTIC CONTINENTAL SHELF 



59 



