THE GEOLOGICAL HISTORY OF NEW YORK STATE 79 
entirely without reference to the underlying rock character and 
structures. Such streams are said to be superimposed because they 
have, so to speak, been let down upon the underlying rock masses. 
To quote Professor Berkey: “ The larger rivers, the great master 
streams, of the superimposed drainage system, in some cases were 
so efficient in the corrasion of their channels that the discovery of 
discordant structures (in the underlying rocks) has not been of 
sufficient influence to displace them, or reverse them, or even to 
shift them very far from their original direct course to the sea. 
They cut directly across mountain ridges because they flowed over 
the plain out of which these ridges have been carved and because 
their own erosive and transporting power have exceeded those of 
any of their tributaries or neighbors.”! Fine examples of such 
superimposed streams which are now entirely out of harmony with 
the structure of the regions over which they flow are the Susque- 
hanna, Delaware, and Hudson. Thus the Susquehanna cuts across 
a whole succession of Appalachian ridges while, in accordance with 
the same explanation, the Delaware cuts through the Kittatinny 
range at the famous Delaware Water Gap. The lower Hudson 
pursues a course no less out of harmony with the structure of the 
country through which it passes. Thus it flows at a considerable 
angle across the Taconic folds above the Highlands, after which 
it passes through a deep gorge which it has cut through the hard 
granites and other rocks of the Highlands. The simple explanation 
is that the Hudson had its course determined upon the surface of 
the upraised’ Cretacic peneplain, and that it has been able to keep 
that course in spite of the discordant structures of the underlying 
rocks. 
But while the great master streams were thus cutting deep 
trenches in hard and soft rock alike, numerous side streams or 
tributaries came into existence and naturally developed along the 
belts of weak rock and in harmony with the geologic structures. 
This is true of all the streams now occupying the valleys between 
the Appalachian ridges. In southeastern New York two remark- 
able cases are presented by the Wallkill river and Rondout creek 
which flow many miles northeastwardly and in a direction almost 
the reverse of that of the Hudson to which they are tributary. As 
the master superimposed Hudson cut its channel deeper and deeper, 
the Wallkill and Rondout side streams were enabled to cut their 
valleys deeper and deeper while they increased in length by pushing 
IN. Y. State Mus. Bul. 146, p. 60. 
