150 NEW YORK STATE MUSEUM 



To this end most of the explorations were made. Two lines less 

 than a mile apart on which a few exploratory borings were made 

 near Springtown indicate two buried channels, a master channel 

 and a tributary from the west which converge northward. A 

 maximum depth reaching 70 feet below sea level was found on the 

 more northerly line almost directly beneath the present stream 

 channel which flows on drift at an elevation of 150 above tide. 



The more southerly profile reaches only sea level indicating a 

 gradient for the preglacial stream at this immediate locality of more 

 tlian 79 feet per mile. 



In the vicinity of Libertyville, 5 to 6 miles farther south, where 

 the aqueduct was finally located, the profile was found to be con- 

 siderably higher. Intermediate profiles are shown in accompany- 

 ing figures. The deepest point yet found on the Libertyville line 

 is 6^ feet above sea level. It is worth noting that the gradient of 

 the ancient Wallkill is therefore shown to be decidedly unsymmet- 

 rical. The rock floor formation remains the same although it may 

 vary somewhat in character. Under these circumstances, however, 

 a gradient of 13 feet per mile from Libert}^nlle to Springtown 

 forms a sharp contrast with the 79 feet per mile represented at 

 the Springtown locality. In view of the remarkable increase of 

 gradient and the narrower form it seems reasonable to regard this 

 as a rejuvenation feature developed at the time of extreme con- 

 tinental elevation. 



How much deeper the lower Wallkill may be. including the so 

 called Rondout river, which is really a continuatic-n of the ancient 

 Wallkill and geologically belongs to this drainage line instead of 

 to the Rondout. no one can tell. But it is at least interesting to 

 observe that the intervening distance from Springtown to the Hud- 

 son at Kingston is approximately 12 miles and that a gradient for 

 that distance equal to the average known in the 6 miles explored, 

 i. e. 24 feet per mile, would depress the outlet 288 feet more. 

 That would be equivalent to 367 feet below sea level. If, how- 

 ever, a steep gradient such as that at Springtown prevails in this 

 lower portion it is necessarily much lower — for example if a 79 

 foot gradient is maintained it would be possible to reach a final 

 outlet at — 1029 feet. It is likely that an intermediate value is 

 more nearly correct. This has. however, an important bearing 

 upon the question of maximum Hudson river depth, especially the 

 existence of an inner deeper gorge above the Highlands. So far 

 as this Wallkill profile goes, it supports the gorge theory. It is 

 certain that the Prepleistocene Wallkill flowed north not very dif- 



