Spencer — Great Canyon of the Hudson River. 5 



American Coast," in 1902,* taking such phenomena as a whole, 

 showed there was accumulative evidence suggesting that these 

 submarine features were gauges for measuring the late great 

 continental elevation. 



The most recent discussion including that of the Hudsonian 

 channel (1904) is in Dr. F. Nansen's epoch-making monograph 

 on continental shelves and previous oscillations of shore lines,f 

 reserved for later consideration. 



The Hudsonian Canyon. 



The channel described by Lindenkohl begins about ten miles 

 off Sandy Hook and extends for 93 miles before it plunges into 

 the canyon. Land miles and not sea miles will be used through- 

 out this paper. At its head, opposite Sandy Hook, the chan- 

 nel is buried by the sand of the coastwise drift-forming bars, 

 though nearer Sew York it is much deeper. Lindenkohl had 

 described the depth of the canyon to 2844 feet below sea level, 

 with a bar in front, and no further information is shown on 

 the IT. S. Coast Survey charts. In revising my last mentioned 

 paper, I found much additional data on the charts issued by the 

 Hydrographic Office, greatly strengthening the evidence of the 

 continuation of the Hudsonian valley, extending down the con- 

 tinental slope to great depths. But on the British charts I 

 made a most astounding find of three soundings of 459, 801 

 and 229 fathoms. The position of the 459 and of the 801 

 soundings of the British chart so closely coincided with those 

 of the Coast Survey chart % at 213 and 345 fathom points that 

 they could not have been represented on the same charts. 

 Thus the British chart showed no barrier to the canyon and 

 very greatly increased the known depth of the narrow gorge, 

 further defined by the 229 fathom point. The extraordinary 

 depth would have been startling had it not been anticipated in 

 all of my long series of analyses of submarine valleys. Both 

 series of soundings were correct, the deeper ones having been 

 made by Lt. Com. Z. L. Tanner§ in 1883 in the Fish Commis- 

 sion steamer Albatross. The older soundings had been 

 retained on the Coast Survey charts. 



The canyon of the Hudson River may now be extended and 

 revised as follows : The mean edge of the continental border 

 may be taken at a depth of 450-500 feet below sea level. The 

 head of the canyon, in a direct line backward of the edge of 



*lb. 



f '' The Bathymetrical Features of the North Polar Seas, with a Discussion 

 of the Continental Shelves and Previous Oscillations of Shore Lines," by 

 Fridtjof Nansen. Quarto, pp, 1-232, plates 28. Published in English by 

 the Fridtjof Nansen Fund for the Advancement of Science, Christiania, 1904. 



% Coast Survey Chart, No. 8. B. A. Chart No. 2480. 



§ Hydrographic Notice to Mariners, No. 56, 1883. 



