TERTIARY WORK IN THE HUDSON VALLEY. 571 



Virginia, and the great valley of eastern Tennessee. The river boldly enters 

 the Highlands and cuts them through from top to bottom, and from side to 

 side. The traditional suggestion of a lake, whose outlet cut down the gorge, 

 or of a cleft in the Highlands by which the lake was drained, is generally 

 offered by more than one of the travellers down the river, if they 

 consider the question at all ; but the possibility of the wasting away of the 

 upper valley-lowland contemporaneously with the cutting down of the 

 narrow gorge is hardly mentioned. Of all explanations, this is by far the 

 most consistent with the other conditions of the problem. There are no 

 signs of fracture of modern date, though there may well be here an ancient 

 fracture line on which the gorge Avould naturally persist in the Tertiary 

 cycle, because all such fractures would have been sought out as valley lines 

 in the Cretaceous and earlier cycles of deep and general denudation. There 

 is no indication of a lake in the upper valley, and, indeed, before any lake 

 could occur there its basin must be provided. The gorge of the Khine below 

 Bingen is truly the outlet of a lake that once occupied the depressed middle 

 portion of that river's course, and the gorge is cut in an uplifted peneplain 

 of denudation ; but this explanation will not apply in the case of the Hudson. 

 The Hudson valley is not of constructional origin ; it is not a warped or 

 broken basin ; every indication gained from the relation of its structure to 

 its form showe^ to be a region of deep denudation ; its ancient constructional 

 topography bears no resemblance to its present form. Excepting the natural 

 hesitation in face of so enormous a piece of work, there seems to be no reason 

 for regarding this valley as an exception to the rule of Appalachian valley- 

 making in general. The upper part must have been excavated only as the 

 lower part was deepened, while the widening of either part depended on the 

 resistance of the rocks in which the valley was sunk. The Hudson valley 

 only repeats with greater emphasis the lesson of the Connecticut valley ; 

 both are carved out of the uplifted Cretaceous peneplain ; both have' an 

 upper open lowland portion, excavated in weak rocks; both turn from the 

 lowland and enter a narrow gorge, cut like a trench in a tract of hard crystal- 

 line rocks. The respective parts are of greater magnitude in the Hudson 

 than in the Connecticut, but the parts are essentially homologous. 



Just as in the case of the Connecticut, the Hudson^gorge in the Highlands 

 is of less and less depth from its upper end near Newburgh to its lower end 

 near Peekskill ; then, curving a little, so as to follow the outcrop of the bot- 

 tom members of the Triassic formation, the river leaves the even-crested 

 Palisades on the right and the eastern division of the crystalline uplands on 

 the left, and the valley becomes progressively shallower as these encl(?siug 

 uplands gradually decrease in height towards the sea, until at New York city 

 they reach sea-level and the valley opens to the ocean. 



Tertiary Work in New Jersey and Pennsylvania : the Delaware and Sus- 



