Spencer — Great Canyon of the Hudson River. 13 



not deeply scored as with atmospheric agents acting for long 

 ages, as would have appeared beneath the superficial mantle 

 had such obtained. One condition might modify this last 

 argument, namely a subsequent long epoch of wave cutting, 

 with the removal of the prominences, such as Nansen describes 

 in his " coast platform " which does not exist here, but in such 

 a case the Hudsonian gorge should have been filled with debris. 



In the region of the Great Lakes from the tilting of beaches, 

 I have worked out great epirogenic movements, and it quite 

 prepares me to expect to find a reduction of the amount of 

 elevation of the continent, represented by the present submer- 

 gence of the valleys along our continental margin due to 

 bending downward of the continental slope, but this would 

 not reduce by any amount that determined in the canyons 

 and the necessary slope of the land surfaces. So also when we 

 find subaerial features submerged, they at least would need to 

 have been depressed to the depth they are now found at, no 

 matter what the cause of depression. 



The canyon section has sunken 6,000-7,000 feet and the 

 valley beyond to 9,000 feet. Did I attempt to guess at the 

 reduction of this amount in the late height of the continent, I 

 should be inclined to pause owing to other features outside the 

 line of this study. But if others wish to reduce the continental 

 elevation by 2,000 feet, by extra bending down of the con- 

 tinental slope, I shall not protest farther than by stating that 

 additional evidence beyond our limit may replace it. Pro- 

 visionally then we may keep the amount of elevation at 9,000 

 feet as shown here, leaving others to correct the figures if found 

 to be excessive. On the other hand, I have no idea that the 

 present heights of the mountains were relatively nearly so great 

 as now. 



Fragments of the Lafayette formation should extend from 

 New Jersey, and underlie the surface of the continental shelf. 

 The great denudation of the region was after the Lafayette 

 period, as was proved by Prof. W. J. McGee. I have found 

 these beds underlying glacial deposits in New Jersey. They 

 are provisionally regarded as Pliocene, unless they are pre- 

 glacial Pleistocene, as thought by Upham. On the surface of 

 the overlying till, rests the Pleistocene Columbia red loams, 

 sands and gravels, in samples not distinguishable from those 

 of the Lafayette formation except in the smaller size of the 

 gravel. And it is such materials which are obtained in the 

 Atlantic city well (Woolman). The denudation of the Lafay- 

 ette has been so extensive that its remains would be more 

 likely outside of a channel, buried as this appears by the 

 Columbia formation, which has levelled over and furnished 

 materials for the surface of the continental shelf before the 





