REPORT ON THE PANAMA CANAL 
201 
The excavation of the Canal, and borings in its bottom show that a 
narrow belt between the two hills is composed of the soft Cucaracha 
beds; yet to the present time there has been no upheaval of the bottom 
of this part of the Canal, nor any other sign to indicate that the hills 
have settled. It is believed, therefore, that the great masses of Gold 
and Contractors Hills are self-supporting and will remain so. There 
is no occasion to raze them. 
CAUSES OF THE SLIDES 
On account of their magnitude, the land slides have received serious 
consideration since the early days of the Canal. But before measures 
for their control are taken up it is necessary briefly to discuss their 
causes. 
The sHdes in the Canal Zone are essentially like many in other parts 
of the w^orld; they are due to the inabihty of the earth or rock to sup- 
port the weight of overlying material. Slow processes of natural 
erosion, rapid cutting by flooded streams and excavations by man fre- 
quently lead to landsHdes. Much of the Canal is cut through weak 
rocks; and in the Culebra District the prism is exceptionally deep. It 
is clear that the conditions there are very favorable for slides. 
The weakness of the rocks is due to several causes: 
Character of the Rocks of the Culebra District. — The rocks of Culebra 
District are of two kinds — stratified and massive. The chief material in- 
volved in the slides is the stratified Cucaracha formation. It is greenish 
grey in color, largely composed of clayey material with some layers of 
rather finely banded volcanic sandstone or tuff, only weakly consoli- 
dated. The Cucaracha beds are limited, along the liae of the Canal, 
to the Culebra District but they have a thickness in places of over 400 
feet. The soft slippery nature of its materials and their loose, uncon- 
solidated condition, make it unusually weak and unable to sustain any 
considerable load. 
The Cucaracha beds alone are responsible for the great slides. The 
Obispo tuff is a rather coarsely f ragmen tal rock, roughly stratified; 
masses of the tuff and of the massive columnar basalt have broken from 
the hills and added some material to the slides, but they have had no 
part in starting them. 
Structural Weakness. — ^The rocks, both stratified and massive, as shown 
by the work of Mr. MacDonald, are cut by numerous faults and this is 
true of the rocks throughout the Gaillard Cut. Where there is a fault, 
the rocks have previously been broken; and therefore, present a place 
