8 Spencer — Great Canyon of the Hudson River. 



greater or less detail does not alter the general features, and 

 the only important points left relate to the question of the can- 

 yon opening out into the valley and its depths, which the 

 analysis shows is 6000-7000 feet, and farther on the charac- 

 teristics are those of a valley rather than a canyon to 9000 

 feet below sea level. 



Surface Channels of the Continental shelf and the Deep one of 

 the Connecticut. 



The surface of the continental shelf is a marvellously flat 

 plain, with a mean slope not exceeding three feet per mile. 

 This condition represents a flat substratum, even though there 

 may be hollows in it levelled over by sand deposits. Nearer 

 than Long Island there is no trace of a moraine either 

 buried or submerged. The surface of the plain is covered 

 over with sea-washed sand, except in the Hudsonian channel. 

 This adjective termination I have long used to designate the 

 drowned sections of the river valleys. The sandy plain is 

 traversed by shallow channels shown on each side of the map 

 at AAAA and BBB. These would be still better followed if 

 more isobathic lines were introduced. It is to a depth of 250 

 feet that these channels are most noticeable. They represent 

 the stream action of an epoch of elevation to this amount since 

 the time of canyon making, and subsequent to the levelling 

 over of the plain after that date. That is to say, these channels 

 absolutely belong to a post-Columbia or Pleistocene epoch, — 

 the canyons to a pre-Columbia or early glacial time. During 

 Columbia oscillations wave action has obliterated all traces of 

 delta form. 



The channel of the Hudson river in crossing the submarine 

 plain shows a bottom of blue clay with sandy material in places. 

 But the course of the old upper channel must have been still 

 defined to have allowed its reopening during the epoch of 

 reelevation of 250 feet just mentioned. 



In the canyon section, the bottom is composed of blue clay 

 with fine sand. Beyond it the continental slope is also surfaced 

 with blue clay or green clay, as shown by many soundings. 



The great Connecticut canyon or valley, asked for by Lin- 

 denkohl,* is represented (at C on the map) by a deep embay- 

 ment, whose west wall is at least 3600 feet high, and it 

 reaches to a depth of 5736 feet below the surface of the sea, 

 but the information is not at hand to define its form, though a 

 canyon perhaps passing into a valley at this point might be 

 expected. 



At D, on the other side of the map, one sees a cove or amphi- 

 theatre such as are commonly indenting the borders of high 

 *Bull. Geol. Soc. Am., vol. xiv, p. 226, 1903. 



L 



