BLASTING FORTY FEET BELOW SEA-LEVEL BEHIND A DIKE
The entrance and intersection of the American and French canals.
A concrete and timber bulkhead, the nearest approach to an orthodox-looking dam a layman can find at Gatun, keeps the water of the sea-level canal out of the lock-chambers. Directly in front of it float three or four high-decked craft that look for all the world like old-time Mississippi River packets. All they seem to lack are a few roustabouts and a gilt trotting-horse between the tall smoke-stacks. As a matter of fact, they are dredges, with living-quarters for the crews. Across the channel behind them, shutting them off from the sea, is a solid-looking clay dike.
“Colonel,” we asked, “how did you put those boats into that mud-puddle,—fly them or jump them over?”
“The dipper-dredge cut the way in, and the suction-dredge closed it behind them. That dike keeps them from being disturbed by the rise and fall of the tide. A great part of the canal between here and Limon Bay was excavated in the dry by steam-shovels working behind dikes forty feet below sea-level; but that was in rock. The stuff these dredges are pumping out is prehistoric sea-bottom—soft, black ooze that runs like oil. A big slide of it started due north toward Limon Bay, swung round to the east, and then due south, went three quarters round the compass, and half-way up the lowest lock-pit. We had to force it out by building the permanent lock-walls right into it, section by section—shoved it out by sheer weight.”
A VIEW (LOOKING NORTH) OF THE UPPER GUARD GATES OF THE PEDRO MIGUEL LOCK
“Is there anything like that under the Gatun Dam?” we asked.
“No, this mud is nearly three quarters of a mile north of it. The entire dam rests on the solidest kind of clay, and the locks are built on a ledge of sandstone, except the north approach wall. That will have to be built on piers driven down through the mud to bed-rock. The approach wall is the continuation of the dividing-wall between the two sets of locks, which projects into what we call the forebay, where ships must come to a stop and make fast to the electric locomotives that will tow them through the locks.