14: Spencer — Great Canyon of the Hudson River. 



re-excavation of the small channels at A AAA and BBB on the 

 map (page 2). These channels as mentioned before, represent 

 a re-elevation of the drowned plain to as much as 250 feet in 

 the later Pleistocene period, since which time the region has 

 been again once or twice depressed, then re-elevated slightly 

 and channelled, and is now sinking at the rate of two feet a 

 century (Prof. Mitch el). All of the changes are remarkable 

 repetitions of those which I have shown to have occurred 

 farther south and in the West Indies. Thus it may be seen 

 that the canyon- making period was in the earlier Pleistocene, 

 and accords with Prof. Dana's views as expressed in the last 

 edition of his Manual, and those of Dr. Upham, only the 

 evidence is in more detail, showing a much greater elevation 

 than was then known. 



I have not touched upon an earlier Tertiary valley, as such 

 could apply only to great depths beyond the canyon section. 



Summary and Conclusion. 



More than 40 years ago, Prof. J„ D. Dana first recognized 

 the submarine extension of the Hudson river in the soundings 

 on the continental shelf. In 1885, Prof. A. Lindenkohl dis- 

 covered the channel suddenly transformed into a canyon near the 

 continental border, reaching to a depth of 2400 feet below the sur- 

 face of submerged plain, which is here about 400 feet beneath sea- 

 level. But near the then known mouth there appeared a great 

 bar. In 1897, I pointed out that the channel was traceable to 

 great depths, which is now proved. A sounding was made 

 near the supposed bar, which has proved to be only a measure- 

 ment taken on the side of a deep canyon with a precipitous 

 wall. Then four miles beyond this point, against another 

 lateral bank, a further sounding reaches to 4800 feet, revealing 

 a canyon 3800 feet in depth, where the continental shelf is 

 not submerged more than 1000 feet. High up on the sides, 

 the gorge here is less than two miles wide, but the incision of 

 the outer canyon into the shelf has a breadth of four miles. 

 At its head, the canyon begins in an amphitheatre, having a 

 descent from 330 feet to 1100 feet in the distance of about a 

 mile. Two more steps of 400 and 500 feet respectively follow. 

 Again between 27. and 31 miles below its head, there is 

 another great step of 2000 feet to the depth of 4800 feet men- 

 tioned. And the gradient below is probably by other great 

 steps. This is just beyond the border of the submarine plain 

 and shows the canyon with a depth of 3800 feet. The canyon 

 is double, a second or more sinuous gorge traverses the outer. 

 A little farther on is a tributary heading in a cove. At 42 miles 

 the canyon begins to widen into a valley, which at 48 miles has 

 a precipitous wall of 2000 feet in height. The valley opens 



