REPORT ON THE PANAMA CANAL 
205 
the adjoining ground could be sluiced along it into the Canal. It would 
provide a main drainage line for the ground on both sides of it, would 
empty the surface ponds and would lower the ground water in adjacent 
sliding material. The pressure of the triangle of ground in the rear of 
the cut against the triangle in front of it would be lessened; and it is 
probable that movement in the forward part of the slide would cease 
sooner than it would otherwise. When the cut is once established it 
offers a second line of defense against the slide by making it possible to 
work along two fronts. 
A somewhat similar cut should be made in the West Culebra Slide. 
It should begin at the main drainage line opposite Culebra Hill and 
extend diagonally from the Canal in a general southerly direction, and 
should drain the existing pond. 
STUDIES FOR THE FUTURE 
In addition to the immediate remedial measures suggested above? 
there are certain observations and protective measures which should 
be undertaken with a view to the future. 
Detection of Movements of Earth or Rock. — A few shdes are now in 
motion, but many more are quiescent. A slide is not necessarily Mead' 
because it has not moved notably for a few years. Its stability may 
hang on a deHcate balance which may be disturbed by some slowly 
developing weakness. There is also a bare possibility that Gold and 
Contractors Hills are not so firmly supported as they are believed to be. 
Repeated surveys of properly placed signals for a number of years to 
come should be made in order: 
(a) To indicate in good time where additional work of prevention is 
needed, to indicate how large a dredging fleet must be kept in readi- 
ness, and to furnish to the engineer of maintenance advance indications 
of emergency conditions. 
(b) To test the effectiveness of remedial measures which may be 
taken to control or prevent slides. These tests would be more sensi- 
tive and definite than the mere occurrence or non-occurrence of slides. 
(c) To furnish a rehable basis for confidence when, in the course of 
time, it appears that the earth and rock movements have so decreased 
that a condition of stabiHty may be inferred. 
Core Borings. — Definite information relative to the rock underlying 
Gold and Contractors Hills is wanting. Many years ago some borings 
were made at stations 500 feet apart along the center line of the Canal, 
some of them to a depth of 40 feet below sea level. 
