ANCIENT WATER LEVELS OF CHAMPLAIN-HUDSON VALLEYS 71 



Gorge of the Hudson. The Hudson river flows in a gorge of 

 more recent age than its valley proper. The gorge, widened out 

 into a well opened valley in the region of the Tappan Sea, is usu- 

 ally elsewhere steep sided, and throughout the middle and upper 

 segments of the river it has a singularly uniform width and hight 

 of wall above sea level. From the head of tide near Troy the rock 

 floor of this gorge is, except for a few islands, below sea level, 

 thus converting the river from near Albany to the sea into a fiord. 

 As this portion of the floor of the gorge is now and has been for 

 some time in the past receiving sediments, its exact depth below 

 sea level is not known. 



Beginning on the south, this gorge is believed to be traceable 

 seav^-ard in the so called submarine extension of the Hudson. Be- 

 tween the 100 and 300 foot fathom lines, the outer, deeper part of 



Fig. 2. Late Cenozoic stage of the Hudson valley. The river with the surrounding- 

 region has been uplifted an undetermined hight above its old base level; the river has 

 cut a deep goi-ge to or near the new base level; the side streams have cut lateral gorges, 

 and the surface of the rock terraces has become roughened by incipient dissection. 

 Approximate preglacial condition of the Hudson river valley. 



the gorge attains a depth of 452 fathoms. If the view be accepted 

 that this part of the gorge has been excavated by the river when 

 the land was higher than it now is, it is necessary to admit that 

 the coast has recently stood 2700 feet higher in relation to the sea. 

 This elevation, if it can be shown to have taken place during the 

 Pleistocene epoch, must have had impor-ftant consequences in the 

 distribution of glaciers and their deposits during epochs of glaci- 

 ation and in the work of streams in the interglacial epochs. Not 

 only the exact geologic epoch or epochs in which this submarine 

 gorge has been excavated is in doubt, but its origin as a subaerial 

 phenomenon has been disputed by eminent writers on the subject 

 of the topography of the continental shelves of the continents. 



Kemarkable examples of these submarine gorges exist on the 

 east shore of the Atlantic ocean off the mouth of the Congo river, 



