6 Spencer — Great Canyon of the Hudson River. 



the shelf, is 20 miles, but its course is somewhat longer. The 

 upper channel has a depth of 42 feet in the very level sandy 

 plain, which is then submerged to only 288 feet (though a hun- 

 dred miles from New York harbor). At this point there is an 

 abrupt descent from the bed of the upper part to 1098 feet in 

 the canyon, within the distance of about a mile. The gorge 

 soon deepens to 1242 feet, where cross section A is taken. 



The canyon extends nearly due east for six miles, where its 

 depth reaches to 1662 feet. It then bends sharply at right 

 angles to the south, and at 12 miles from its head a narrow 

 inner gorge descends from 1770 to 2292 feet (in a distance of 

 1*5 miles) where the broad outer canyon attains a depth of only 

 1500 feet below sea level. Here the shelf is submerged about 

 250 feet, accordingly the outer and inner canyons have respec- 

 tive depths to 1250 and 2050. A cross section is shown in 

 figure E (added since paper went to press) which is located near 

 the soundings of 2292 feet shown on the map and longitu- 

 dinal section. Here the canyon turns again at nearly right 

 angles towards the east, though farther on it bends slightly 

 southeastward. A depth of 2640 feet is reached in 18 miles, 

 where cross section B is taken. At 23 miles the depth is 2844 

 feet, and at 26*5 miles is the position of the 213-fathom sound- 

 ing, which was supposed to have indicated a bar, and close 

 against which is the discovered sounding of 459 fathoms, as 

 shown in the precipitous wall in cross section C. Nearly 

 midway between these soundings is one of 457 fathoms (the 

 last two not being situated quite in the center of the channel). 

 These, with others on record, but not shown on the published 

 charts, form a chain of soundings from one to two miles apart 

 reaching to near the floor of the inner gorge, thus establishing 

 its continuity. At this locality also, unpublished soundings 

 further show the double canyon, the outer of which, with a 

 breadth of four miles, is revealed to a depth of 1200-1300 feet 

 below sea level, while the inner has a width, not exceeding 

 one mile but reaches to over 2800 feet. The gradi- 

 ents and depths of the canyon and their relation to sea level 

 are shown in the longitudinal section figure 1. At 31 miles the 

 801 fathoms is found, close against that of 345 fathoms not 

 shown on map. This last is on the side of the gorge, of 

 3800 feet, where the continental slope is further submerged 

 1000 feet. Here, too, is a great downward pitch in the gradient 

 of 2000 feet in four miles. At this point the maximum 

 breadth of the gorge, nearly 3800 feet above the floor of the 

 canyon, does not exceed two miles, with the bottom necessarily 

 narrower. Seemingly part of the slope of the wall where the 

 deep sounding was found approaches 60 degrees. At 34 miles 

 there is a short tributary from the north, heading in a typical 



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