208 HAUPT—DEEPER NAVIGABLE CHANNELS. [April 2, 
It is referred to in the early Coast Survey Reports, and was made 
the subject of a special paper by the late honored member of this 
Society, Prof. Henry Mitchell, who prepared a manuscript report 
upon it, in connection with the physics of the lower bay, in 1858, 
but which was not published. It serves to confirm the claims of 
this paper that depths may be and frequently are the result of eddy- 
ing action rather than velocity. The confluence of three currents 
produces a resultant having a northeasterly set which impinges upon 
the bar at the head of Gedney’s Channel and is deflected thence 
by this resisting bank of sand northwardly, boring out the slue for 
a length of a mile and a width of a half mile. The latest survey 
shows a depth of fifty-three feet, with but eighteen feet on either 
flank. It was proposed at one time to change the direction of this 
resultant by cutting off one of its components and training the cur-~ 
rents seaward to open Gedney’s Channel by the utilization of this 
force, but it was not accepted. Again, the reaction at the head of 
Sandy Hook has produced a maximum depth of sixty-eight feet, 
diminishing within about a mile to thirty feet, while abreast of the 
point and a half mile distant the depth is but sixteen feet. 
The construction of the old Breakwater at the mouth of the Del- 
aware in 1828 furnishes some instructive lessons as to the changes 
effected by obstacles placed in a tideway. Here, at the ends of the 
ice-breaker and of the breakwater, are to be found the character- 
istic deep holes resulting from the head generated by the resisting 
structures. At the gap the pockets are on the outside of the open- 
ing, and the depths are the effects of the flood-tide. Both of these 
pockets are fifty feet deep, and the material scoured out from them 
has been carried into the harbor and deposited in the lee of the 
structures, making a shoal with only ten feet at one point. At the 
southeastern end of the breakwater the ebb reaction has scoured to 
a depth of fifty-four feet, while at the western end of the ice- breaker 
the hole is due to the flood, and is limited to about forty feet. 
Moreover, the diagrams of velocity curves show that in the centre 
of the harbor, where the maximum velocity of the ebb is six feet 
per second, the bottom has not been prevented from shoaling to 
about fifteen feet, while a similar ebb velocity at the ‘‘ gorge’”’ is 
able to maintain depths of thirty feet. If these depths are due 
solely to velocities they should be equal, since like causes should 
produce like effects. 
Numerous other instances of these abnormal depths due to reac- 
