200 
REPORT ON THE PANAMA CANAL 
are possible, but because of the slope and increased distance from the 
Canal such possible additions would be in decreasing volume. Gold 
Hill Hmits the slide to the south. 
THE SOLIDITY OF THE HILLS OF CULEBRA DISTRICT 
In addition to the danger of the sKdes, is there danger that the Canal 
may be blocked by the fall of the hills of Culebra District? 
These hills are composed of intrusive bodies of basalt, or of masses 
of the hard Obispo tuff commonly associated with basalt in this dis- 
trict. So far as can be judged from present exposures, they do not rest 
on the soft Cucaracha formation, but extend far into the earth, and are 
self-supporting. Rock may slough off from them, but there is no evi- 
dence that they will collapse. 
Culebra and Zion Hills. — The hard tuff' of Culebra Hill practically 
limits the West Culebra Slide in front of it. Cracks have formed in the 
tuff and it is probable that some of the rock will break off as the slide 
settles. Zion Hill is a basaltic intrusion, and much rock has fallen from 
its face; more may follow. But the total amount that may fall will 
only make a relatively small addition to the upper part of the West 
Culebra Slide. 
Gold and Contractors Hills. — Gold and Contractors Hills rise steeply 
from the banks of the Canal, for 410 feet and 260 feet above the bottom 
of the Canal, respectively; and then slope more gently to their summits. 
They are nearly, but not exactly, opposite each other. Gold Hill is 
chiefly composed of basalt, which formerly spread out near its top, and 
was partially supported on the softer Cucaracha formation. When the 
East Culebra and Cucaracha sHdes became active the support was re- 
moved, and a large mass of the basalt fell from the northern and south- 
ern sides of the hill. The lower part of Gold Hill on the side towards 
the Canal is made up of hard Obispo tuff, bounded by a basalt dike, and 
there is httle danger that it will yield. 
Contractors Hill is of hard Obispo tuff, which is separated from the 
Cucaracha by a fault which dips into the hill at an angle of 60 or 70 
degrees with the horizontal. There is a possibility that this part of the 
hill depends more for its support on the Cucaracha beds than seems 
probable, and as a measure of precaution all reasonable means should 
be taken to keep the Cucaracha beds in place; and, especially, the fault 
fissure should be kept closed to prevent water seeping in. If the bor- 
ings, suggested later, to reveal the underground structure, show that 
these precautions are unnecessary they can be discontinued. 
