GEOLOGY OF THE NEW YORK CITY AQUEDUCT 95 



tained for the next inner one — inside of holes no. lo and no. 22 

 — there would be room for only one more and its approximate 

 depth would lie somewhere between 800 feet and 900 feet below 

 tide. 



Recent drilling has shown a marked difference between holes 

 no. 10 and no. 22. Hole no. 10 located 500 feet southeast of no. 

 22 is nearly 100 feet deeper. Since no. 10 is nearly straight down 

 stream this discrepancy is disturbing. But if one considers the 

 distance of each from the east bank it is noted that no. 10 is 900 

 feet out and no. 22 is 800 feet. Hole no. 10 is thus about 100 

 feet nearer the middle of the stream and allowing for this addi- 

 tional distance according to the profile as known it ought to be 

 at least 70 feet deeper than no. 22. This corrected difference then 

 of 30 feet does not seem to be of much importance. 



Summary. Everywhere in its lower course the Hudson ex- 

 hibits the character of a narrow gorge, sometimes of a gorge within 

 a gorge, most of which is either submerged or buried several hun- 

 dred feet. 



Depths of 200 to 300 feet are average and for the last 60 miles 

 of its course represent widths of 1000 to 3000 feet. 



Greater depths are believed to be maintained continuously within 

 a narrower inner notch, but of this there is no conclusive proof 

 and very little evidence outside of a few Storm King borings. 



The Storm King-Breakneck notch is over 751 feet deep. But 

 it is abnormal at least in width and probably also in depth, due to 

 ice erosion. 



The conditions indicate (a) rapid stream erosion while the con- 

 tinent stood much higher than now, (/?) glaciation which enlarged 

 the gorge in at least a few places and filled it with rock debris 

 and later with mud during submergence, (c) finally an emergence 

 with minor oscillations and erosion to the present time. 



J 

 4 Origin of the present course of the Hudson 



The course of the Hudson is in most respects no more abnormal 

 than that of the Susquehanna. Both flow across mountain ridges 

 in such manner as to indicate their superimposed character. Both 

 date back to the Gretaceous peneplain. But the striking feature 

 of the Hudson is its straight course. As Hobbs and others have 

 pointed out, the river is abnormally straight for more than 200 

 miles — and this in spite of the fact that it crosses the bedding and 

 other structures of the country rock at nearly all points at an 



