10 Spencer — Great Canyon of the Hudson River. 



the canyon on the continental border. Here then, in its upper 

 portion, the gorge penetrates easily denuded material, though 

 some of the beds are composed of remarkably tough clay. 

 Where the sides of the canyon are so precipitous as was shown 

 at the 459 and 801-fathom isobaths, we may suppose that the 

 lower portions are cut out of the harder older rocks, succeeded 

 by more yielding material farther down the submarine valley. 



Origin of the Canyon 



It appears that the previous students of the submarine chan- 

 nel have all had the idea that it was formerly a land valley. 

 Such analysis of the phenomena as has been given must be used 

 in discussing its origin under any other hypothesis. While a few 

 other soundings are desirable for fuller local details, we need 

 not one more for a reasonably full discussion of the principles 

 involved — only enough are wanting to stimulate interest in a 

 revision. Not to speak of similar phenomena farther south and 

 in the West Indies discovered by myself,* and those since 

 brought to light and systematized in a brilliant manner by 

 Prof. Edward Hull of London, situated on the eastern side of 

 the Atlantic basin, f I shall mention the canyon of the Congo 

 discovered by Stassano, and worked out by Mr. J. Y. Buchanan 

 and described by Mr. Edward Stallibrass, and the canyon off 

 Cape Yerde described by Mr. Henry Benest, on account of the 

 completeness of detail of such features, not hitherto obtained, 

 but with which the Hudsonian canyon can now be grouped with 

 the advantage of our knowledge of the surrounding physiograph- 

 ical and geological environments, and with the further interest 

 in that it is situated at the main door of the continent. 



If formed by river action, the Hudsonian canyon affords 

 proof of startling physical conditions of the region, at a very late 

 date, and hence the whole interest in its origin, for if now a 

 land feature, it would be one of not such unusual occurrence 

 as to awaken our amazement. Can the views of the earlier 

 writers be challenged ? The only other possible causes of its 

 origin seem to be : — (1) submarine glacial erosion, (2) open 

 faults, (3) submarine rivers, and (4) a remnant of a primitive 

 depression. This last would only be suggested by an obstinate 

 objector to its iluviatile origin, or one unfamiliar with the 

 analyses of such subjects; for after passing the Paleozoic 

 evolution of the continent, what is now its great slope should 

 be covered with detritus carried into the sea during the long 

 period of denudation of the Mesosoic era, thus obscuring older 

 depressions. Some of the African canyons have been attrib- 



*" Reconstruction of the Antillean Continent" and other papers in Bull. 

 Geol. Soc. Am. and in Quar. Jour. Geol. Soc. London, 

 f Published by the Victoria Institute, London. 



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